MATfluids is an open source library for processing fluid flow data, be it from experimental acquisition or numerical simulation. The package is consistently updated to go beyond a classical analysis (i.e. vorticity, strain rate, particle advection, etc.) and include modern and powerful techniques in the field such as proper orthogonal decomposition, dynamic mode decomposition and the finite-time Lyapunov exponent. Currently, MATfluids is compatible with MATLAB and mostly compatible with Octave.