  We study extension of scalars for sheaves of vector spaces, assembling
results that follow from well-known statements about vector spaces, but also
developing some complements. In particular, we formulate Galois descent in this
context, and we also discuss the case of derived categories and perverse
sheaves. Most of the results are not new, but our aim is to give an accessible
introduction to this subject relying only on techniques from basic sheaf
theory. Our proofs also illustrate some applications of results about the
structure of constructible and perverse sheaves.
