Star tracking at Ball Aerospace has reached a new level of performance with the development of the High Accuracy Star Tracker (HAST). This new tracker builds on the experience gained from the Chandra Aspect Camera which attained better than 0.2 arc-seconds on-orbit overall performance with a stationary star field. The HAST is optimized to achieve similar performance on stars moving between 0.07 and 1.0 degrees/second and can maintain track on stars moving 0 to 4 degrees/second. HAST is capable of tracking multiple stars, further enhancing the accuracy performance. This paper examines the principal error components that affect star tracking accuracy. We further examine the physical basis for three error sources: 1) boresight alignment bias, 2) transit dependent bias, and 3) random measurement. We develop the design trade space used to optimize tracker performance within these error constraints. Finally, we present the working specifications for HAST, describe the HAST implementation, and review the flight qualification test results.