Metallic matrices are essential constituents for fabrication of metal-matrix composites (MMCs). This article describes the three different classes of aluminum alloys, namely, commercial aluminum alloys, low-density and high-modulus alloys, and high temperature alloys. It presents typical tensile properties and fracture toughness of selected heat treatable aluminum alloys in a table. Titanium alloys are very attractive for MMC applications, due to their higher strength and temperature capability compared to aluminum alloys. The article tabulates the effect of heat treatment on room-temperature properties and tensile properties of Ti-25Al-17Nb alloy sheet.