1 Introduction.- The Sedimentary Record: Volcanic Contribution.- Chemical Composition of Tephra.- Types of Pyroclastic Accumulations.- 2 Volcanoes, Volcanic Rocks and Magma Chambers.- Tectonic Setting of Volcanoes.- Form of Volcanoes.- Origin of Magmas and Classification of Volcanic Rocks.- Magma Chambers.- 3 Magmatic Volatiles and Rheology.- Volatiles.- Rheology.- Vesiculation.- 4 Explosive Volcanic Eruptions.- Types of Volcanic Activity.- Types of Eruptions.- Pyroclastic Eruptive Systems.- Hydroclastic Eruptive Processes.- Volcanic Energy.- 5 Pyroclastic Fragments and Deposits.- General Components.- Vitric Particles and Pyrogenic Crystals.- Structure.- Texture.- 6 Subaerial Fallout Tephra.- Components of Subaerial Fallout.- Areal Distribution.- Structures.- Fabric.- Size Parameters.- Eolian Fractionation.- 7 Submarine Fallout Tephra from Subaerial Eruptions.- Chemical Composition.- Structures of Submarine and Lacustrine Ash Layers.- Areal Thickness Distribution and Volume.- Grain Size and Sorting.- Regional Distribution and Tephrochronology.- 8 Pyroclastic Flow Deposits.- Historic Development of Concepts.- The Deposits.- Classification and Nomenclature.- The Flows.- Ignimbrite Vents: Speculation.- 9 Deposits of Hydroclastic Eruptions.- Definition of Terms.- Components of Hydroclastic Deposits.- Structures.- Base Surge Deposits.- Maar Volcanoes.- Littoral Cones.- Peperites.- 10 Submarine Volcaniclastic Rocks.- Deep Water Stage.- Shoaling Submarine Volcano.- Transition Submarine — Subaerial.- Volcaniclastic Aprons.- Silicic Submarine Eruptions.- Subaqueous Pyroclastic Flows.- Nonwelded Deposits.- Welded Deposits.- 11 Lahars.- Debris Flows as Fluids.- Distribution and Thickness.- Surface of Lahars.- Basal Contact of Lahars.- Components of Lahars.- Grain-Size Distribution.- Vesicles.- Grading.- Fabric.- Comparison of Lahars with Other Kinds of Coarse-Grained Deposits.- Origin.- 12 Alteration of Volcanic Glass.- Diagenesis.- Alteration of Basaltic Glass.- Alteration ofSilicic Glass.- 13 Stratigraphic Problems of Pyroclastic Rocks.- Relation of Volcanic Activity to Rock Stratigraphy.- Tephrochronology.- Volcanic Facies.- Stratigraphic Examples.- 14 Pyroclastic Rocks and Tectonic Environment.- Convergent Margins, Magmatic Arcs, and Sedimentation.- The Pre-Cambrian.- References.- Locality Index.