This paper presents the rationale for increasing the resistance factor for concrete in compression in the 2004 edition of the Canadian Standards Association (CSA) standard A23.3, Design of concrete structures, from 0.60 to 0.65 and for precast concrete produced in CSA-certified plants from 0.65 to 0.70. The new values are supported by a probability-based resistance factor calibration and an investigation of their impact in the context of current American standards and past editions of A23.3. The work was initiated because parameters for the rectangular concrete stress block introduced in the 1994 edition of A23.3 give smaller factored resistances for concretes with strengths between 20 and 40 MPa. Minimum target reliability indices for components that fail suddenly are maintained using the new resistance factors. In the regions of compressive force – bending moment interaction diagrams that are controlled by the resistance factor for concrete, the factored resistances computed using the 2004 edition of A23.3 are similar to those of current American design criteria.Key words: code calibration, compression-initiated failure, concrete, interaction diagram, rectangular stress block, ultimate limit state.