Concrete produced with high fly ash replacement levels is considered high volume fly ash (HVFA) concrete. One of the main limitations to the increased usage of HVFA concrete is the lack of familiarity with its setting time and strength development at various curing temperatures. A laboratory testing program was developed to quantify the effect of fly ash dosage, fly ash chemical composition, cement chemical composition, and environmental conditions on the hydration development, setting times, and compressive strength development of HVFA concrete. Concretes were made with 35% and 50% fly ash replacement levels (by volume) with four fly ash sources (two Class C and two Class F). Setting times are delayed with an increase in fly ash dosage and when the fly ash CaO content is increased for a given fly ash dosage. As the fly ash dosage is increased, the heat generated per volume of concrete decreases. An increase in the fly ash CaO content for a given fly ash dosage, results in increased in-place temperatures. HVFA concrete made with Class C fly ash exhibits a higher rate of early-strength development when compared to the Class F fly ash concrete. HVFA concrete can be produced to have comparable setting times and early-age compressive strength development to conventional concrete.