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The focus of High Temperature Superconducting (HTS) microwave circuit development has now shifted to improving the high power handling capability. This paper reviews our latest results in this area including: HTS material improvement; new concepts and rules for HTS high power circuit design; and the latest high power filter test results. For HTS materials, the surface resistance versus rf magnetic field test results and the third harmonic test results for both YBa/sub 2/Cu/sub 3/O/sub 7/ and Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ thin films are presented. For HTS microwave circuits, novel design concepts and rules for high power HTS filters are discussed. Several compact planar HTS filters were designed, fabricated, packaged and tested. The performance of a 3-pole, 1.3% equal-ripple bandwidth planar HTS filter showed no measurable degradation for transmitted power levels up to 74 watts at 77 K. The performance of a 2-pole, 1% equal-ripple bandwidth planar HTS filter showed no measurable degradation for transmitted power levels up to 115 watts at 77 K. To our knowledge, these test results represent the highest power handling of compact planar HTS filters operating at 77 K, sufficient for use in telecommunication transmitters.