Objective: To introduce a new ophthalmic optical coherence tomography technology that allows unprecedented simultaneous ultra-high speed and ultra-high resolution. Methods: Using a superluminescent diode source, a clinically viable ultra-high speed, ultra-high resolution spectral domain optical coherence tomography system was developed. Results: In vivo images of the retina, the optic nerve head, and retinal blood flow were obtained at an ultra-high speed of 34.1 microseconds (ms) per A-scan, which is 73 times faster than commercially available optical coherence tomography instruments. Single images (B-scans) consisting of 1000 A-scans were acquired in 34.1 ms, allowing video rate imaging at 29 frames per second with an axial resolution of 6 μm. Using a different source in a slightly slower configuration, single images consisting of 500 A-scans were acquired in 34 ms, allowing imaging at 29 frames per second at an axial resolution of 3.5 μm, which is 3 times better than commercially available optical coherence tomography instruments. The amount of energy directed into the eye in both cases, 600 μW, is less than that of the Stratus OCT3 and is safe for intrabeam viewing for up to 8 hours at the same retinal location. Conclusion: Spectral domain optical coherence tomography technology enables ophthalmic imaging with unprecedented simultaneous ultra-high speed and ultrahigh resolution. ©2005 American Medical Association. All rights reserved.