This paper deals with the irradiation creep behavior of Zr-base alloys, both under normal operating and power transient conditions. The first part is devoted to the creep experiments, which were conducted in the OSIRIS or SILOE metallurgical test reactors using argon internally pressurized cladding tubes to simulate the normal operating conditions in PWRs. The studied materials are the following Zr-base alloys: stress-relieved (SRA) and fully recrystallized (RXA) low tin Zircaloy-4, the RXA Zr-SnFeV M4 alloy and the FRAMATOME-ANP Zr-l%NbO (M5™). The effects of the alloy composition and metallurgical condition, temperature (280 to 380°C), stress level (0 to 120 MPa), and fast neutron flux (1 to 2 × 1018 n/m2s, E > 1 MeV) on the irradiation creep kinetics are discussed. These irradiation creep results confirm the lower creep rate of RXA Zy-4, M4, and M5™ with respect to SRA Zy-4. In the second part, this paper relates to the clad behavior under pellet-cladding interaction conditions. To this end, a specific irradiation device operated at a nominal temperature of 350°C is used to strain a cladding tube sample at high stress level (about 400 MPa by internal pressure) and under neutron flux (2 × 1018 n/m2s, E > 1 MeV). The diameter elongation is measured online versus time. The results are compared to those obtained during out-of-pile creep tests on irradiated specimens using similar temperature and stress conditions. This experiment allows discussion of the contribution of irradiation-induced creep with respect to the thermal creep at high stress levels relevant to PCI conditions.