Stanford University hosted the XIX International Symposium on Lepton and Photon Interactions at High Energies on August 9 – 14, 1999, at the Law School on the Stanford University Campus, the site of the previous Symposia. This volume constitutes the proceedings of the Symposium.Contents:Reports from the B Factories:CESR and CLEO (K Honscheid)Status of KEKB Accelerator and Detector, BELLE (F Takasaki)Status of PEP-II and BaBar (J Dorfan)HERA-B Status (M Medinnis)Brief Report from the Tevatron (M Paulini)Heavy Flavor Physics and CP Violation:Heavy Quark Decays (R A Poling)Heavy Quark Lifetimes, Mixing, and CP Violation (G Blaylock)ε'/ε Results from KTeV (E Blucher)Results on Direct CP Violation from NA48 (G Barr)A Status Report of KLOE at DAΦNE (S Bertolucci)Quark Mixing Matrix Studies and Lepton Flavor Violation Searches Using Rare Decays of Kaons (W Molzon)Tau Physics (A Pich)B Decays, the Unitarity Triangle, and the Universe (A F Falk)Neutrino Physics:Solar Neutrinos (Y Suzuki)Atmospheric Neutrinos and the Oscillations Bonanza (W A Mann)Accelerator and Reactor Neutrino Experiments (L DiLella)Neutrino Mass and Oscillations (R G H Robertson)Electroweak Interactions and Beyond:Precision Electroweak at the Z (M L Swartz)Electroweak Measurements from Hadron Machines (M Lancaster)Precise Electroweak Results from LEP2 (D G Charlton)R Values in Low Energy e+e- Annihilation (Z-G Zhao)Status of the Muon (g – 2) Experiment (B L Roberts)Ten Years of Precision Electroweak Physics (A Sirlin)New Particle Searches (V Ruhlmann-Kleider)Recent Developments in Physics Beyond the Standard Model (G F Giudice)Structure Within Particles:Structure Functions in Deep Inelastic Lepton-Nucleon Scattering (M Klein)Diffraction and the Pomeron (H Abramowicz)The Spin Structure of the Nucleon (G K Mallot)Structure of the Photon (J M Butterworth)Rare Φ Decays and Exotic Hadrons (S I Serednyakov)Q Phenomena and Theory:Fragmentation and Hadronization (B R Webber)Test of Perturbative Q and Jet Physics (J Womersley)Applications of Q (M Beneke) Lattice Calculations and Hadron Physics (S Aoki)Cosmology and Astrophysics:Dark Matter Searches (B Sadoulet)Supernovae, Dark Energy, and the Accelerating Universe: The Status of the Cosmological Parameters (S Perlmutter)High Energy Particles from the Universe (R A Ong)Cosmic Microwave Background: Past, Future, and Present (S Dodelson)Looking to the Future:Physics Needs for Future Accelerators (J D Lykken)R&D Progress Toward Future Linear Colliders (G-A Voss)Towards Very High Energy Accelerators (J S Wurtele)Gravity, Particle Physics and Their Unification (J M Maldacena)Assessment and Outlook (B Richter)Readership: High-energy, astro-, nuclear, experimental and theoretical physicists.Key Features:Review articles from experts such as A Khrennikov, T Hida and K E GustafsonAn up-to-date account of the latest development in the field