Simple way to increase total laser power at the target is combining of multiple beams from a laser array. For incoherent operation of N lasers, an on-axis intensity in the far-field can be increased N times. By establishing coherence across the N lasers in the array, additional N-times gain in the on-axis intensity can be achieved. Known techniques for optical coupling arrangement between lasers in the array are overviewed with analysis of their advantages and shortcomings. Principal causes for reduction of far-field on-axis intensity from laser arrays are discussed demonstrating necessity to seek compromise conditions between high laser array efficiency and optical quality of a combined beam.