Is it better to stretch before or after a workout?

The simple answer is both are beneficial. Before a workout it is good to perform Active (warm-up) stretching and corrective stretching. Active stretching involves movements where you assume a position and then hold it with no assistance other than the strength of the muscles holding the position (agonist muscles). The tension of the muscles holding the position help relax the muscles being stretched (antagonists). Active stretches are usually only held for about 10-15 seconds. Many of the movements in Yoga can be considered active stretches. Corrective stretching is also good before a workout because it addresses specific muscles and helps to improve imbalances in the body while working out. Corrective stretching is performed primarily when someone has been assessed by a professional for flexibility and muscle imbalances. Post-workout stretching is good to help aid in recovery and maintain muscle length.