High power lasers (HPLs) are ubiquitous in industry (laser cutting/welding), defense (missile defense), energy (laser fusion), and basic science (as a pump for more advanced systems). While most applications benefit from higher power levels, the output of an individual laser is limited by thermal effects that degrade the efficiency and distort the the beam quality. An approach to circumvent this is via the process of coherently combining smaller powers from multiple lasers with definite phase relations to enhance the total power. I demonstrated coherent beam combination (CBC) of a large number (21) of elements by using active phase control. While the initial experiment utilized an expensive multi-order diffraction grating as the combining element, I realized the same combining efficiency through free-space interference. By utilizing coupled-mode theory, I designed a mask that achieved an equally high performance at a tiny fraction of the cost.