Objectives: The shear bond strengths of five bonding systems to human dentin, ground and uncut enamel were compared. Methods: The uncut enamel surface of extracted human teeth were lightly cleaned with non-fluoridated pumice (Preppies, Whip-Mix). The ground enamel and dentin surfaces were prepared by lightly grinding the surface with 600-grit SiC paper just before bonding. The specimens were randomly assigned into groups and stored in water. Three self-etching bonding systems and two phosphoric acid-etch bonding systems were used according to manufacturers' instructions: Peak SE + Peak LC (Ultradent), Prompt-L-Pop (3M ESPE), Clearfil SE (Kuraray), PQ1+phosphoric acid etch (Ultradent), Peak LC+phosphoric acid etch. The bonding systems were used randomly. Filtek Z100 (3M ESPE) was cured to all the specimens using the Ultradent bonding jig. The specimens were placed into a 37°C water bath for 24 hours before they were thermal cycled for 2,000 cycles at 5°C and 55°C. After thermal cycling, they were placed back into a 37°C water bath for 24 hours. The experiment was repeated three times with 10 teeth used for each bonding system on each of the three surfaces (total 30 teeth per bonding system on each surface). The results were compared with ANOVA and Fishers PLSD test (α=0.05). Results: On ground enamel, the conventional etch followed by Peak LC (40.7 MPa) and Peak SE + Peak LC (38.3 MPa) produced the best shear bond strengths. On the uncut enamel, the conventional etch systems produced the best shear bond strength. On dentin, only Prompt-L-Pop produced significantly lower shear bond strengths (p<0.05). Conclusions: All the bonding systems produced greater bond strengths to ground rather than uncut enamel. The acid-etch bonding systems delivered the greatest bond strengths to dentin, ground and uncut enamel. This research was supported by NSERC and an unrestricted research grant from Ultradent.