This paper evaluates the Achilles exoskeleton. The exoskeleton is intended to provide push-off assistance for healthy subjects during walking. The assistance is provided by a series elastic actuator that has been optimized to provide maximal push-off power. The paper presents the control method of the exoskeleton and the evaluation of the exoskeleton. Benchtop tests evaluated the performance of the actuator and human experiments evaluated the working of the complete system. The actuator can track force reference signals with amplitudes of 1 N to 100 N with a bandwidth between 8.1 Hz and 20.6 Hz, and outputs a maximum mechanical power of 80.2 W. Based on these results the augmentation factor predicted that the exoskeleton can generate a 33 W decrease in metabolic cost. In contrast with this prediction, in the human experiments we found an increase in metabolic rate for assistance (21.2 W) and no assistance (22.7 W) compared to baseline.