Abrikosov Lattice --- AC Josephson Effect --- Accelerators --- Accretion --- Accretion Disks --- Acoustics --- Active Galaxies --- Adsorption --- Advection --- Advection-Dominated Accretion --- Aerosols --- Aether --- Affleck-Dine Mechanism --- Afshar's Experiment --- AGB Stars --- Aharonov-Bohm Effect --- Aharonov-Casher Effect --- Algebra--- Algebraic Geometry --- Algebraic Stacks --- Alloys --- Alpha Particles --- Amphiphilic Aggregates and Membranes --- Analysis (Mathematics) --- Analyticity --- Andreev States --- Angular Momentum --- Anisotropy of the Cosmic Background --- Anisotropy of the Cosmic Microwave Background --- Annealing (Quantum) --- Antibracket Formalism --- Anti-DeSitter Space --- Antiferromagnetism --- Antimatter --- Anyons --- Aperiodic Order --- Arithmetic Lattices --- Ashtekar Variables --- Aspon Model --- Asteroids --- Asteroseismology --- Astrobiology --- Astronomy --- Astrophysical Background Radiation --- Astroparticle Physics --- Astrophysical Jets --- Asymptotic Freedom --- Asymptotic Giant Branch --- Atiyah-Singer Theorem --- Atmosphere --- Atmospheric Electricity --- Atmospheric Optics --- Atmospheric Refraction --- Atomic Force Microscopy --- Atoms --- Auger Processes --- Axinos --- Axions