Experiments have been performed to determine the effect of loading rate and temperature on the fracture toughness of both granular and S2 columnar freshwater ice. Loading rate was varied from 0.04 to 40.0 kPam s-1 , and over this range the fracture toughness was observed to decrease from 201 to 109 kPam. Examination of load—CMOD curves indicate that at a loading rate of 40 kPam s-1 , the crack tip plasticity was sufficiently limited that the specimen behavior can be considered linear elastic, thus providing a valid Kq measurement. When test temperature was varied from −5 to −45°C for the S2 columnar ice, no significant variation in toughness was observed. In contrast, for granular ice, a higher toughness (144 kPam) was observed in the −5 to −20°C range than for the S2 columnar ice. However, the toughness of the granular ice at−45°C is not significantly different from that of the S2 columnar ice. A companion paper (Weber and Nixon, 1996) analyzes the results in greater detail comparing them with previous work, and presents a detailed fractographic analysis of the failure surfaces.