The solid solutions of ${alpha}-Si_3N_4$, i.e. ${alpha}$-sialons, are represented by a general formula of $M_x(Si,Al)_{12}(O,N)_{16}$, in which metal ions (M) dissolve into interstitial sites to stabilize the structure. Processing methods for the fabrication of ${alpha}/{eta}$-sialon composites, ${alpha}-sialon/{eta}Si_3N_4$ composites, refractory or tough ${alpha}$-sialon ceramics have been developed to tailor the mechanical properties. Translucent and photoluminescent properties have been investigated recently. A number of applications of ${alpha}$-sialon ceramics as engineering and optical ceramics are also presented.