Isogeometric analysis is a new method for the numerical simulation of problems governed by partial differential equations. It possesses many features in common with finite element methods (FEM) but takes some inspiration from Computer Aided Design tools. We illustrate how quasi-interpolation methods can be suitably used to set Dirichlet boundary conditions in isogeometric analysis. In particular, we focus on quasi-interpolant projectors for generalized B-splines, which have been recently proposed as a possible alternative to NURBS in isogeometric analysis. (C) 2010 Elsevier B.V. All rights reserved.