M Theory --- Machine Learning --- MACHOs --- Macromolecules --- Macroscopic Quantum Effects --- Magellanic Clouds --- Magnetic Fields --- Magnetism --- Magnetoelectronics --- Magnetohydrodynamics --- Magnetoresistance --- Magnetorheological Effect --- Magnetosphere --- Main Sequence Stars --- Maldacena Conjecture --- Manganites --- Manifolds --- Mansuripur's Paradox --- Many Body Problem --- Many Worlds Interpretation of Quantum Mechanics --- Marked Point Processes --- Markets --- Markov Processes --- Mars --- Martensites --- Masers --- Mass --- Massive Stars --- Master Equation --- Material Science --- Mathematics --- Matrix Algebra --- Matter-Antimatter Asymmetry --- Maxwell's Demon --- Mechanics --- Meissner-Ochsenfeld Effect (Meissner Effect) --- Melts --- Membranes --- Memory Circuit-Elements --- Memory of Materials --- Mercury-Manganese Stars --- Mercury (planet) --- Mesons --- Mesoscopic Systems --- Metallicity (Astronomy) --- Metals --- Metamaterials --- Metastability --- Meteorites --- Metric --- Metric Spaces --- Michelson-Morley Experiment --- Microscopy --- Milan Factor --- Milky Way --- Mineralogy --- Minihadrons --- Minimal Surfaces--- Minimally Supersymmetric Standard Model --- Minkowski Functionals --- Miras --- Mirror Symmetry --- Mirrors --- Mittag-Leffler Functions Mixmaster Universe --- Moduli --- Molecular Beam Epitaxy --- Molecular Dynamics --- Molecules --- MOND --- Monopole --- Monster Group --- Monte Carlo Method --- Moon --- Moonshine Theory (maths) --- Morse Theory --- Motives --- Mott Insulators --- Multiferroics --- Multigravity Theory --- Multigrid Methods --- Multiplier Ideals --- Multiquarks --- Multiresolution Analysis --- Multiverse Cosmology --- Muon Colliders --- Muonium --- Muons