diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index aff088f..820641b 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -23,6 +23,7 @@ jobs:
       fail-fast: false
       matrix:
         version:
+          - '1.9'
           - 'lts'
           - '1'
         os:
diff --git a/Project.toml b/Project.toml
index 76f3d20..0e984b1 100644
--- a/Project.toml
+++ b/Project.toml
@@ -10,12 +10,21 @@ LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 QuadGK = "1fd47b50-473d-5c70-9696-f719f8f3bcdc"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 
+[weakdeps]
+ITensorMPS = "0d1a4710-d33b-49a5-8f18-73bdf49b47e2"
+ITensors = "9136182c-28ba-11e9-034c-db9fb085ebd5"
+
+[extensions]
+TCIITensorConversion = ["ITensors", "ITensorMPS"]
+
 [compat]
 BitIntegers = "0.3.5"
 EllipsisNotation = "1"
+ITensorMPS = "0.2, 0.3"
+ITensors = "0.6, 0.7, 0.8, 0.9"
 QuadGK = "2.9"
-Random = "1.10.0"
-julia = "1.6"
+Random = "1.9.0"
+julia = "1.9"
 
 [extras]
 Aqua = "4c88cf16-eb10-579e-8560-4a9242c79595"
@@ -28,4 +37,4 @@ Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 Zygote = "e88e6eb3-aa80-5325-afca-941959d7151f"
 
 [targets]
-test = ["Aqua", "Test", "Random", "ITensors", "Zygote", "Optim", "QuanticsGrids", "JET"]
+test = ["Aqua", "Test", "Random", "ITensors", "ITensorMPS", "Zygote", "Optim", "QuanticsGrids", "JET"]
diff --git a/docs/Project.toml b/docs/Project.toml
index 6270074..8cbf9b4 100644
--- a/docs/Project.toml
+++ b/docs/Project.toml
@@ -1,5 +1,7 @@
 [deps]
 Documenter = "e30172f5-a6a5-5a46-863b-614d45cd2de4"
+ITensorMPS = "0d1a4710-d33b-49a5-8f18-73bdf49b47e2"
+ITensors = "9136182c-28ba-11e9-034c-db9fb085ebd5"
 LaTeXStrings = "b964fa9f-0449-5b57-a5c2-d3ea65f4040f"
 Plots = "91a5bcdd-55d7-5caf-9e0b-520d859cae80"
 TensorCrossInterpolation = "b261b2ec-6378-4871-b32e-9173bb050604"
diff --git a/docs/make.jl b/docs/make.jl
index 5bfce32..b63d640 100644
--- a/docs/make.jl
+++ b/docs/make.jl
@@ -1,10 +1,21 @@
 using TensorCrossInterpolation
+using ITensors
+using ITensorMPS
 using Documenter
 
-DocMeta.setdocmeta!(TensorCrossInterpolation, :DocTestSetup, :(using TensorCrossInterpolation); recursive=true)
+preamble = quote
+    using TensorCrossInterpolation
+    using ITensors
+    using ITensorMPS
+end
+
+DocMeta.setdocmeta!(TensorCrossInterpolation, :DocTestSetup, preamble; recursive=true)
 
 makedocs(;
-    modules=[TensorCrossInterpolation],
+    modules=[
+        TensorCrossInterpolation,
+        Base.get_extension(TensorCrossInterpolation, :TCIITensorConversion)
+    ],
     authors="Ritter.Marc <Ritter.Marc@physik.uni-muenchen.de> and contributors",
     sitename="TensorCrossInterpolation.jl",
     format=Documenter.HTML(;
@@ -14,7 +25,7 @@ makedocs(;
     pages=[
         "Home" => "index.md",
         "Documentation" => "documentation.md",
-        "Implementation details" => "implementation.md"
+        "Extensions" => "extensions.md",
     ]
 )
 
diff --git a/docs/src/extensions.md b/docs/src/extensions.md
new file mode 100644
index 0000000..9d98f89
--- /dev/null
+++ b/docs/src/extensions.md
@@ -0,0 +1,17 @@
+# Extensions
+
+This page documents extensions to [TensorCrossInterpolation](https://github.com/tensor4all/TensorCrossInterpolation.jl).
+
+Currently, there is only one extension, TCIITensorConversion.
+
+## TCIITensorConversion
+
+Dependencies:
+- [ITensors.jl](https://github.com/ITensor/ITensors.jl)
+- [ITensorMPS.jl](https://github.com/ITensor/ITensorMPS.jl)
+
+This module is automatically loaded when ITensors and ITensorMPS are present in addition to TensorCrossInterpolation. It offers conversion constructors between ITensorMPS types and TensorCrossInterpolation types, and an analogue of the [`evaluate`](@ref) function for ITensor types.
+
+```@autodocs
+Modules = [Base.get_extension(TensorCrossInterpolation, :TCIITensorConversion)]
+```
diff --git a/ext_disabled/TCIITensorConversion.jl b/ext/TCIITensorConversion/TCIITensorConversion.jl
similarity index 53%
rename from ext_disabled/TCIITensorConversion.jl
rename to ext/TCIITensorConversion/TCIITensorConversion.jl
index e293456..e08c219 100644
--- a/ext_disabled/TCIITensorConversion.jl
+++ b/ext/TCIITensorConversion/TCIITensorConversion.jl
@@ -1,10 +1,14 @@
 module TCIITensorConversion
 
 import TensorCrossInterpolation as TCI
+import TensorCrossInterpolation: evaluate
+
 using ITensors
+import ITensorMPS
+import ITensorMPS: MPS, MPO
 
-export MPS
-export evaluate_mps
+export MPS, MPO
+export evaluate
 
 include("ttmpsconversion.jl")
 include("mpsutil.jl")
diff --git a/ext/TCIITensorConversion/mpsutil.jl b/ext/TCIITensorConversion/mpsutil.jl
new file mode 100644
index 0000000..7bf8c5c
--- /dev/null
+++ b/ext/TCIITensorConversion/mpsutil.jl
@@ -0,0 +1,50 @@
+@doc raw"""
+    function evaluate(
+        mps::Union{ITensorMPS.MPS,ITensorMPS.MPO},
+        indexspecs::Vararg{AbstractVector{<:Tuple{ITensorMPS.Index,Int}}}
+    )
+
+Evaluates an MPS or MPO for a given set of index values.
+
+- `indexspec` is a list of tuples, where each tuple contains an `ITensorMPS.Index` object specifying an index, and an `Int` corresponding to the value of the specified index.
+
+If many evaluations are necessary, it may be advantageous to convert your MPS to a [`TensorCrossInterpolation.TTCache`](@ref) object first.
+"""
+function evaluate(
+    mps::Union{ITensorMPS.MPS,ITensorMPS.MPO},
+    indexspecs::Vararg{AbstractVector{<:Tuple{ITensors.Index,Int}}}
+)
+    if isempty(indexspecs)
+        error("Please specify at which indices you wish to evaluate the MPS.")
+    elseif any(length.(indexspecs) .!= length(mps))
+        error("Need one index per MPS leg")
+    end
+
+    V = ITensor(1.0)
+    for j in eachindex(indexspecs[1])
+        states = prod(ITensorMPS.state(spec[j]...) for spec in indexspecs)
+        V *= mps[j] * states
+    end
+    return scalar(V)
+end
+@doc raw"""
+    function evaluate(
+        mps::Union{ITensorMPS.MPS,ITensorMPS.MPO},
+        indices::AbstractVector{<:ITensors.Index},
+        indexvalues::AbstractVector{Int}
+    )
+
+Evaluates an MPS or MPO for a given set of index values.
+
+- `indices` is a list of `ITensors.Index` objects that specifies the order in which indices are given.
+- `indexvalues` is a list of integer values in the same order as `indices`.
+
+If many evaluations are necessary, it may be advantageous to convert your MPS to a [`TensorCrossInterpolation.TTCache`](@ref) object first.
+"""
+function evaluate(
+    mps::Union{ITensorMPS.MPS,ITensorMPS.MPO},
+    indices::AbstractVector{<:ITensors.Index},
+    indexvalues::AbstractVector{Int}
+)
+    return evaluate(mps, collect(zip(indices, indexvalues)))
+end
diff --git a/ext_disabled/ttmpsconversion.jl b/ext/TCIITensorConversion/ttmpsconversion.jl
similarity index 56%
rename from ext_disabled/ttmpsconversion.jl
rename to ext/TCIITensorConversion/ttmpsconversion.jl
index 7b39175..11d2f0d 100644
--- a/ext_disabled/ttmpsconversion.jl
+++ b/ext/TCIITensorConversion/ttmpsconversion.jl
@@ -1,15 +1,4 @@
-
-"""
-    MPS(tt, siteindices...)
-
-Convert a tensor train to an ITensor MPS
-
- * `tt`            Tensor train
- * `siteindices`   Arrays of ITensor Index objects.
-
- If `siteindices` is left empty, a default set of indices will be used.
-"""
-function ITensors.MPS(tt::TCI.TensorTrain{T}; sites=nothing)::MPS where {T}
+function ITensorMPS.MPS(tt::TCI.TensorTrain{T}; sites=nothing)::MPS where {T}
     N = length(tt)
     localdims = [size(t, 2) for t in tt]
 
@@ -30,11 +19,21 @@ function ITensors.MPS(tt::TCI.TensorTrain{T}; sites=nothing)::MPS where {T}
     return MPS(tensors_)
 end
 
-function ITensors.MPS(tci::TCI.AbstractTensorTrain{T}; sites=nothing)::MPS where {T}
-    return MPS(TCI.tensortrain(tci), sites=sites)
+"""
+    MPS(tt::TCI.AbstractTensorTrain{T}; sites=nothing)
+
+Convert a tensor train to an `ITensorMPS.MPS`.
+Arguments:
+- `tt`: The tensor train to be converted.
+- `siteindices`: An array of ITensor Index objects, where `sites[n]` corresponds to the index for the nth site.
+
+If `siteindices` is left empty, a default set of indices will be generated.
+"""
+function ITensorMPS.MPS(tt::TCI.AbstractTensorTrain{T}; sites=nothing)::MPS where {T}
+    return MPS(TCI.tensortrain(tt), sites=sites)
 end
 
-function ITensors.MPO(tt::TCI.TensorTrain{T}; sites=nothing)::MPO where {T}
+function ITensorMPS.MPO(tt::TCI.TensorTrain{T}; sites=nothing)::ITensorMPS.MPO where {T}
     N = length(tt)
     localdims = TCI.sitedims(tt)
 
@@ -57,22 +56,32 @@ function ITensors.MPO(tt::TCI.TensorTrain{T}; sites=nothing)::MPO where {T}
     tensors_[1] *= onehot(links[1] => 1)
     tensors_[end] *= onehot(links[end] => 1)
 
-    return MPO(tensors_)
+    return ITensorMPS.MPO(tensors_)
 end
 
-function ITensors.MPO(tci::TCI.AbstractTensorTrain{T}; sites=nothing)::MPO where {T}
-    return MPO(TCI.tensortrain(tci), sites=sites)
+"""
+    MPO(tt::TCI.AbstractTensorTrain{T}; sites=nothing)
+
+Convert a tensor train to an `ITensorMPS.MPO`.
+Arguments:
+- `tt`: The tensor train to be converted.
+- `sites`: An array of arrays of ITensor Index objects, where `sites[n][m]` corresponds to the mth index attached to the nth site.
+
+If `siteindices` is left empty, a default set of indices will be generated.
+"""
+function ITensorMPS.MPO(tci::TCI.AbstractTensorTrain{T}; sites=nothing)::ITensorMPS.MPO where {T}
+    return ITensorMPS.MPO(TCI.tensortrain(tci), sites=sites)
 end
 
 
 """
-    function TCI.TensorTrain(mps::ITensors.MPS)
+    function TensorTrain(mps::ITensorMPS.MPS)
 
-Converts an ITensor MPS object into a TensorTrain. Note that this only works if the MPS has a single leg per site! Otherwise, use [`TCI.TensorTrain(mps::ITensors.MPO)`](@ref).
+Converts an `ITensorMPS.MPS` object into a TensorTrain. Note that this only works if the MPS has a single leg per site. Otherwise, use [`TensorCrossInterpolation.TensorTrain(mps::ITensorMPS.MPO)`](@ref).
 """
-function TCI.TensorTrain(mps::ITensors.MPS)
-    links = linkinds(mps)
-    sites = siteinds(mps)
+function TCI.TensorTrain(mps::ITensorMPS.MPS)
+    links = ITensorMPS.linkinds(mps)
+    sites = ITensors.SiteTypes.siteinds(mps)
     Tfirst = zeros(ComplexF64, 1, dim(sites[1]), dim(links[1]))
     Tfirst[1, :, :] = Array(mps[1], sites[1], links[1])
     Tlast =  zeros(ComplexF64, dim(links[end]), dim(sites[end]), 1)
@@ -87,15 +96,15 @@ function TCI.TensorTrain(mps::ITensors.MPS)
 end
 
 """
-    function TCI.TensorTrain(mps::ITensors.MPO)
+    function TensorTrain(mps::ITensorMPS.MPO)
 
-Convertes an ITensor MPO object into a TensorTrain.
+Converts an `ITensorMPS.MPO` object into a [`TensorCrossInterpolation.TensorTrain`](@ref).
 """
-function TCI.TensorTrain{V, N}(mpo::ITensors.MPO; sites=nothing) where {N, V}
-    links = linkinds(mpo)
+function TCI.TensorTrain{V, N}(mpo::ITensorMPS.MPO; sites=nothing) where {N, V}
+    links = ITensorMPS.linkinds(mpo)
     if sites === nothing
-        sites = siteinds(mpo)
-    elseif !all(issetequal.(siteinds(mpo), sites))
+        sites = ITensors.SiteTypes.siteinds(mpo)
+    elseif !all(issetequal.(ITensors.SiteTypes.siteinds(mpo), sites))
         error("Site indices do not correspond to the site indices of the MPO.")
     end
 
diff --git a/ext_disabled/mpsutil.jl b/ext_disabled/mpsutil.jl
deleted file mode 100644
index 7e2cf91..0000000
--- a/ext_disabled/mpsutil.jl
+++ /dev/null
@@ -1,25 +0,0 @@
-function TCI.evaluate(
-    mps::Union{ITensors.MPS,ITensors.MPO},
-    indexspecs::Vararg{AbstractVector{<:Tuple{ITensors.Index,Int}}}
-)
-    if isempty(indexspecs)
-        error("Please specify at which indices you wish to evaluate the MPS.")
-    elseif any(length.(indexspecs) .!= length(mps))
-        error("Need one index per MPS leg")
-    end
-
-    V = ITensor(1.0)
-    for j in eachindex(indexspecs[1])
-        states = prod(state(spec[j]...) for spec in indexspecs)
-        V *= mps[j] * states
-    end
-    return scalar(V)
-end
-
-function TCI.evaluate(
-    mps::Union{ITensors.MPS,ITensors.MPO},
-    indices::AbstractVector{<:ITensors.Index},
-    indexvalues::AbstractVector{Int}
-)
-    return TCI.evaluate(mps, collect(zip(indices, indexvalues)))
-end
diff --git a/test/runtests.jl b/test/runtests.jl
index 768cb06..0cf3ca8 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -21,3 +21,6 @@ include("test_conversion.jl")
 include("test_contraction.jl")
 include("test_integration.jl")
 include("test_globalsearch.jl")
+
+# TCIITensorConversion extension
+include("test_TCIITensorConversion.jl")
diff --git a/test/test_TCIITensorConversion.jl b/test/test_TCIITensorConversion.jl
new file mode 100644
index 0000000..e3ed726
--- /dev/null
+++ b/test/test_TCIITensorConversion.jl
@@ -0,0 +1,100 @@
+using Test
+
+import TensorCrossInterpolation as TCI
+import TensorCrossInterpolation: evaluate
+using ITensors
+using ITensorMPS
+
+@testset "TCIITensorConversion.jl" begin
+    @testset "TT to MPS conversion" begin
+        tt = TCI.TensorTrain([rand(1, 4, 4), rand(4, 4, 2), rand(2, 4, 7), rand(7, 4, 1)])
+        mps = ITensorMPS.MPS(tt)
+        @test ITensorMPS.linkdims(mps) == [4, 2, 7]
+    end
+
+    @testset "TT to MPO conversion and back" begin
+        tt = TCI.TensorTrain([rand(1, 4, 3, 4), rand(4, 2, 4, 2), rand(2, 5, 1, 7), rand(7, 9, 4, 1)])
+        mpo = ITensorMPS.MPO(tt)
+        @test ITensorMPS.linkdims(mpo) == [4, 2, 7]
+        @test dim.(siteinds(mpo)[1]) == [4, 3]
+        @test dim.(siteinds(mpo)[2]) == [2, 4]
+        @test dim.(siteinds(mpo)[3]) == [5, 1]
+        @test dim.(siteinds(mpo)[4]) == [9, 4]
+
+        tt2 = TCI.TensorTrain{Float64,4}(mpo)
+        @test all(tt2[i] == tt[i] for i in 1:length(tt))
+
+        sites = reverse.(siteinds(mpo))
+        ttreverse = TCI.TensorTrain{Float64,4}(mpo, sites=sites)
+        @test all(permutedims(ttreverse[i], [1, 3, 2, 4]) == tt[i] for i in 1:length(tt))
+    end
+
+    function binary_representation(index::Int, numdigits::Int)
+        return Int[(index & (1 << (numdigits - i))) != 0 for i in 1:numdigits]
+    end
+
+    @testset "mps util" begin
+        @testset "one mps evaluation" begin
+            m = 5
+            mps = MPS(m)
+            linkindices = [Index(2, "link") for i in 1:(m-1)]
+            mps[1] = ITensor(
+                ones(2, 2),
+                Index(2, "site"),
+                linkindices[1]
+            )
+            for i in 2:(m-1)
+                mps[i] = ITensor(
+                    ones(2, 2, 2),
+                    linkindices[i-1],
+                    Index(2, "site"),
+                    linkindices[i]
+                )
+            end
+            mps[m] = ITensor(
+                ones(2, 2),
+                linkindices[m-1],
+                Index(2, "site")
+            )
+
+            for i in 1:(2^m)
+                q = binary_representation(i, m) .+ 1
+                @test evaluate(mps, siteinds(mps), q) == 2^(m - 1)
+                @test evaluate(mps, collect(zip(siteinds(mps), q))) == 2^(m - 1)
+            end
+        end
+
+        @testset "delta mps evaluation" begin
+            m = 5
+            mps = MPS(m)
+            linkindices = [Index(2, "link") for i in 1:(m-1)]
+            mps[1] = ITensor(
+                [i == j for i in 0:1, j in 0:1],
+                Index(2, "site"),
+                linkindices[1]
+            )
+            for i in 2:(m-1)
+                mps[i] = ITensor(
+                    [i == j && j == k for i in 0:1, j in 0:1, k in 0:1],
+                    linkindices[i-1],
+                    Index(2, "site"),
+                    linkindices[i]
+                )
+            end
+            mps[m] = ITensor(
+                [i == j for i in 0:1, j in 0:1],
+                linkindices[m-1],
+                Index(2, "site")
+            )
+
+            for i in 1:(2^m)
+                q = binary_representation(i, m) .+ 1
+                @test evaluate(mps, siteinds(mps), q) == all(q .== first(q))
+                @test (
+                    evaluate(mps, collect(zip(siteinds(mps), q))) ==
+                    all(q .== first(q))
+                )
+            end
+        end
+    end
+end
diff --git a/test/test_mpsutil.jl b/test/test_mpsutil.jl
deleted file mode 100644
index b963759..0000000
--- a/test/test_mpsutil.jl
+++ /dev/null
@@ -1,68 +0,0 @@
-function binary_representation(index::Int, numdigits::Int)
-    return Int[(index & (1 << (numdigits - i))) != 0 for i in 1:numdigits]
-end
-
-@testset "mps util" begin
-    @testset "one mps evaluation" begin
-        m = 5
-        mps = ITensors.MPS(m)
-        linkindices = [ITensors.Index(2, "link") for i in 1:(m-1)]
-        mps[1] = ITensors.ITensor(
-            ones(2, 2),
-            ITensors.Index(2, "site"),
-            linkindices[1]
-        )
-        for i in 2:(m-1)
-            mps[i] = ITensors.ITensor(
-                ones(2, 2, 2),
-                linkindices[i-1],
-                ITensors.Index(2, "site"),
-                linkindices[i]
-            )
-        end
-        mps[m] = ITensors.ITensor(
-            ones(2, 2),
-            linkindices[m-1],
-            ITensors.Index(2, "site")
-        )
-
-        for i in 1:(2^m)
-            q = binary_representation(i, m) .+ 1
-            @test TCI.evaluate(mps, ITensors.siteinds(mps), q) == 2^(m - 1)
-            @test TCI.evaluate(mps, collect(zip(ITensors.siteinds(mps), q))) == 2^(m - 1)
-        end
-    end
-
-    @testset "delta mps evaluation" begin
-        m = 5
-        mps =ITensors.MPS(m)
-        linkindices = [ITensors.Index(2, "link") for i in 1:(m-1)]
-        mps[1] = ITensors.ITensor(
-            [i == j for i in 0:1, j in 0:1],
-            ITensors.Index(2, "site"),
-            linkindices[1]
-        )
-        for i in 2:(m-1)
-            mps[i] = ITensors.ITensor(
-                [i == j && j == k for i in 0:1, j in 0:1, k in 0:1],
-                linkindices[i-1],
-                ITensors.Index(2, "site"),
-                linkindices[i]
-            )
-        end
-        mps[m] = ITensors.ITensor(
-            [i == j for i in 0:1, j in 0:1],
-            linkindices[m-1],
-            ITensors.Index(2, "site")
-        )
-
-        for i in 1:(2^m)
-            q = binary_representation(i, m) .+ 1
-            @test TCI.evaluate(mps, ITensors.siteinds(mps), q) == all(q .== first(q))
-            @test (
-                TCI.evaluate(mps, collect(zip(ITensors.siteinds(mps), q))) ==
-                all(q .== first(q))
-            )
-        end
-    end
-end
diff --git a/test/test_ttmpsconversion.jl b/test/test_ttmpsconversion.jl
deleted file mode 100644
index f879e18..0000000
--- a/test/test_ttmpsconversion.jl
+++ /dev/null
@@ -1,22 +0,0 @@
-@testset "TT to MPS conversion" begin
-    tt = TCI.TensorTrain([rand(1, 4, 4), rand(4, 4, 2), rand(2, 4, 7), rand(7, 4, 1)])
-    mps = ITensors.MPS(tt)
-    @test ITensors.linkdims(mps) == [4, 2, 7]
-end
-
-@testset "TT to MPO conversion and back" begin
-    tt = TCI.TensorTrain([rand(1, 4, 3, 4), rand(4, 2, 4, 2), rand(2, 5, 1, 7), rand(7, 9, 4, 1)])
-    mpo = ITensors.MPO(tt)
-    @test ITensors.linkdims(mpo) == [4, 2, 7]
-    @test ITensors.dim.(ITensors.siteinds(mpo)[1]) == [4, 3]
-    @test ITensors.dim.(ITensors.siteinds(mpo)[2]) == [2, 4]
-    @test ITensors.dim.(ITensors.siteinds(mpo)[3]) == [5, 1]
-    @test ITensors.dim.(ITensors.siteinds(mpo)[4]) == [9, 4]
-
-    tt2 = TCI.TensorTrain{Float64,4}(mpo)
-    @test all(tt2.T .== tt.T)
-
-    sites = reverse.(ITensors.siteinds(mpo))
-    ttreverse = TCI.TensorTrain{Float64,4}(mpo, sites=sites)
-    @test all(permutedims.(ttreverse.T, Ref([1, 3, 2, 4])) .== tt.T)
-end