High Power Optical Amplifiers (HPOAs) are key components in high-bandwidth, free-space communication systems. In many applications, these HPOAs must be highly-reliable, which leads to specific design choices. Erbium/Ytterbium co-doped cladding-pumped gain stages provide high power and efficiency. Some of the design choices and key results will be described. Amplifiers with output power exceeding 10 W and fundamental spatial-mode output will be described.