The crystallization kinetics of amorphous 3 and 8 mol% yttria stabilized zirconia (3YSZ and 8YSZ) thin films grown by pulsed laser deposition (PLD), spray pyrolysis and dc-magnetron sputtering are explored. The deposited films were heat treated up to 1000°C ex situ and in situ in an X-ray diffractometer. A minimum temperature of 275°C was determined at which as deposited amorphous PLD grown 3YSZ films fully crystallize within five hours. Above 325°C these films transform nearly instantaneously with a high degree of micro-strain when crystallized below 500°C. In these films the t'' phase crystallizes which transforms at T > 600°C to the t' phase upon relaxation of the micro-strain. Furthermore, the crystallization of 8YSZ thin films grown by PLD, spray pyrolysis and dc-sputtering are characterized by in situ XRD measurements. At a constant heating rate of 2.4 K/min crystallization is accomplished after reaching 800°C, while PLD grown thin films were completely crystallized already at ca. 300°C.