In this chapter, we discuss the problem of effective loss of composite materials. These problems attract attention due to the potential utility of ferroelectric materials in high frequency tunable devices, see, e.g., [331, 394]. Although the problem is known for a long time, it has not been investigated completely, see, e.g., [12, 330, 350]. Probably, it is impossible solve this problem in explicit form in the general case. However, in the special cases it can be solved.