From Wikipedia:
Maddux's best season was likely in 1995 when he finished 19-2 with an incredible 1.63 ERA in a year when the overall National League ERA was 4.23. In the strike-shortened 1994 season, he had an even lower ERA of 1.56, the best single-season ERA among currently-active pitchers, which compared even more favorably to the NL in that year (4.26), but had a 16-6 record. His career ERA is 3.00, second only to Pedro Martínez among all active starting pitchers. From 1993-1998, Maddux led the National League in ERA four times, and was second the other two seasons. Since the introduction of the "lively ball" in 1920, there have only been five pitchers to have full-season ERAs under 1.65: Luis Tiant and Bob Gibson in the anomalous 1968 season, Dwight Gooden in 1985, and Greg Maddux, twice (1994 and 1995).