In the past 25 years, many researchers studied nonlinear time domain simulation methods of free surface and floating body motions based on the potential theory. These simulation methods are called as numerical wave tank (NWT). To solve the simultaneous equations of ideal fluid motion and floating body motion, rational NWT solves both the velocity field and the acceleration field. This review paper presents theoretical and technological state of NWT. The basic mathematical formulation of NWT for floating body simulation is firstly given. Then, the application of NWTs for two dimensional and three dimensional problems are presented and the strengths and limitations of NWT is explained. The direction of future development 3D-NWT is also discussed.