We study some theoretical aspects of Legendre polynomial chaos based finite element approximations of elliptic and parabolic linear stochastic partial differential equations (SPDEs) and provide a priori error estimates in tensor product Sobolev spaces that hold under appropriate regularity assumptions. Our analysis takes place in the setting of finitedimensional noise, where the SPDE coefficients depend on a finite number of second-order random variables. We first derive a priori error estimates for finite element approximations of a class of linear elliptic SPDEs. Subsequently, we consider finite element approximations of parabolic SPDEs coupled with a θ-weighted temporal discretization scheme. We establish conditions under which the time-stepping scheme is stable and derive a priori rates of convergence as a function of spatial, temporal, and stochastic discretization parameters. We later consider steady-state and time-dependent stochastic diffusion equations and illustrate how the general results provided here can be applied to specific SPDE models. Finally, we theoretically analyze primal and adjoint-based recovery of stochastic linear output functionals that depend on the solution of elliptic SPDEs and show that these schemes are superconvergent. KEY WORDS: stochastic partial differential equations, a priori error estimation, chaos expansions, finite element methods, time-stepping stability, functional approximation * Correspond to Prasanth B. Nair,We shall now introduce the finite-dimensional subspaces V h ⊂ V and S p ξ ⊂ S used for the numerical approximation of (4) and (9). First, let T be a triangulation of the domain D consisting of a finite collection of triangles (resp. tetrahedra) T i such that T i ∩ T j = ∅ for i = j, i T i = D, and such that no vertex lies in the interior of an edge (resp. a face) of another triangle (resp. tetrahedron). We consider a family of triangulations T h with mesh-size h ∈ [0, 1[, which are supposed to be nondegenerate, i.e., there exists a constant µ > 0 such that diam(B T ) ≥ µ diam(T ), for all T ∈ T h and h ∈ [0, 1[, where B T is the largest ball contained in T , and such that max diam(T ), T ∈ T h ≤ h diam(D).