The GPstuff toolbox is a versatile collection of Gaussian process models and computational tools required for inference. The tools include, among others, various inference methods, sparse approximations and model assessment methods. The GPstuff toolbox works (at least) with Matlab versions r2009b (7.9) or newer (older versions down to 7.7 should work also, but the code is not tested with them). Most of the functionality works also with Octave (3.6.4 or newer, see release notes for details). Most of the code is written in m-files but some of the most computationally critical parts have been coded in C.