The silicides have obvious atractive characteristics that make them promising materials as thermoelectric energy converters. The constituting elements are abundant and have low price, many of compounds have good high temperature stability. Therefore, considerable eforts have been made, especially in the past 10 years, in order to develop eicient silicide-based thermoelectric materials. These eforts have culminated in creation of Mg 2 (Si-Sn) n-type thermoelectric alloys with proven maximum thermoelec-tric igure of merit ZT of 1.3. This success is based on combination of two approaches to maximize the thermoelectric performance: the band structure engineering and the alloying. In this chapter, we review data on crystal and electronic structure as well as on the thermoelectric properties of Mg 2 X compounds and their solid solutions.