diff --git a/src/Ansatz/Chain.jl b/src/Ansatz/Chain.jl
index bf5517a..d567b09 100644
--- a/src/Ansatz/Chain.jl
+++ b/src/Ansatz/Chain.jl
@@ -559,3 +559,19 @@ function expect(ψ::Chain, observables)
 
     return contract(tn)
 end
+
+overlap(a::Chain, b::Chain) = overlap(socket(a), a, socket(b), b)
+
+# TODO fix optimal path
+function overlap(::State, a::Chain, ::State, b::Chain)
+    @assert issetequal(sites(a), sites(b)) "Ansatzes must have the same sites"
+
+    b = copy(b)
+    b = @reindex! outputs(a) => outputs(b)
+
+    tn = merge(TensorNetwork(a), TensorNetwork(b'))
+    return contract(tn)
+end
+
+overlap(a::Product, b::Chain) = overlap(convert(Chain, a), b)
+overlap(a::Chain, b::Product) = overlap(a, convert(Chain, b))
diff --git a/src/Ansatz/Product.jl b/src/Ansatz/Product.jl
index c5f613f..21b89b1 100644
--- a/src/Ansatz/Product.jl
+++ b/src/Ansatz/Product.jl
@@ -54,3 +54,13 @@ function LinearAlgebra.normalize!(::Union{State,Operator}, tn::Product, p::Real)
     end
     tn
 end
+
+overlap(a::Product, b::Product) = overlap(socket(a), a, socket(b), b)
+
+function overlap(::State, a::Product, ::State, b::Product)
+    @assert issetequal(sites(a), sites(b)) "Ansatzes must have the same sites"
+
+    mapreduce(*, zip(tensors(a), tensors(b))) do (ta, tb)
+        dot(parent(ta), conj(parent(tb)))
+    end
+end
diff --git a/src/Qrochet.jl b/src/Qrochet.jl
index 1c88052..2f5f365 100644
--- a/src/Qrochet.jl
+++ b/src/Qrochet.jl
@@ -24,9 +24,8 @@ export MPS, pMPS, MPO, pMPO
 export leftindex, rightindex, isleftcanonical, isrightcanonical
 export canonize_site, canonize_site!, truncate!
 export canonize, canonize!, mixed_canonize, mixed_canonize!
-export expect
 
-export evolve!
+export evolve!, expect, overlap
 
 # reexports from Tenet
 using Tenet