Abstract
 In the present chapter, the principles of the boundary element methods for 
phase change problems over domains with fixed boundaries are developed briefly. 
The details are developed starting from the 1-D diffusion problems over domains 
with fixed boundaries subjected to different types of boundary and initial conditions. 
In these problems, a new criterion has emerged: the existence of a moving 
boundary, which requires special treatment when solving overall problems. 
Keywords: Boundary elements methods, phase change problems, moving boundary problems, Stefan condition.

