In this paper we propose time-varying FIR equalization techniques for multiple-input multiple-output (MIMO) transmission over doubly selective channels. The doubly selective channel is modeled using the basis expansion model (BEM), and equalized by means of time-varying FIR filters. The time- varying FIR filters are also modeled using the BEM. By doing this, the time-varying deconvolution problem is converted into a two-dimensional time-invariant deconvolution problem in the time-invariant coefficients of the channel BEM and the time- invariant coefficients of the equalizer BEM. The time-varying FIR equalizers are derived based on the matched filtering criterion, as well as the minimum mean-squared error (MMSE) and the zero-forcing (ZF) criteria. The performance of the MMSE and ZF equalizers in the context of MIMO transmission is demonstrated by numerical simulations.