AECL has extensive experience on in-reactor corrosion and crud deposition on Zircaloy fuel cladding. Results and observations from fuel cladding irradiated in commercial Canadian pressurized heavy water (PHW) reactors and experiments conducted in the NRX and NRU reactor loops at Chalk River are summarized. Corrosion was monitored by weight gain measurements on coupons irradiated in the reactor loops and zirconium oxide film thickness measurements from metallographic examination of fuel cladding. The effects of coolant chemistry on Zircaloy corrosion were reviewed with emphasis on the use of ammonia dosing to suppress radiolytic oxygen production in two-phase coolants. Crud deposition on irradiated fuel cladding was assessed from visual observations, measurements of deposit weight, deposit thickness and from chemical and x-ray analyses. The effects of coolant chemistry, heat flux and crud concentration in both single-phase and two-phase coolants were the main parameters studied.