A positive operator A and a closed subspace 𝓢 of a Hilbert space ℋ are called compatible if there exists a projector Q onto 𝓢 such that AQ = Q*A. Compatibility is shown to depend on the existence of certain decompositions of ℋ and the ranges of A and $A^{1/2}$. It also depends on a certain angle between A(𝓢) and the orthogonal of 𝓢.