A randomization test (RndT) is a statistical significance test for which the validity is based on the random assignment of experimental units in a designed experiment. In a random sampling setting, it can also be applied in a very general way because its validity does not rely on distributional assumptions, homogeneity of variances, or independence of errors. However, the use of RndTs did not receive much attention in applied research because RndTs rely on computationally intensive algorithms and most popular and common statistical software packages do not provide facilities to easily perform randomization tests. In order to fill this gap, we present a software package, RT4Win. Unlike most stand-alone software and programs for RndTs, RT4Win is a fast Windows-based program with a user-friendly interface. It provides a facility to carry out RndTs in a series of experimental designs, for both systematic and Monte Carlo data partition methods. The program is free of charge and available upon request from the authors.