Abstract Pennsylvanian and Lower Permian organic carbonate buildups mostly lack large massive reef-building organisms, but rather were constructed by relatively small organisms, such as calcareous algae, calcisponges, and bryozoans, Microbial encrustation and submarine cementation often played significant roles in the construction of the buildups. These buildups consist of a spectrum of mound and reef types whose organic and inorganic compositions are controlled mainly by seawater temperature and light availability, which in turn are related directly to paleolatitude and/or water depth, and growth position. Lower Upper Carboniferous (Bashkirian-lower Moscovian, Morrowan-lower Desmoinesian), shallow shelf to shelf-margin, organic carbonate buildups are mostiy broad low banks and mounds constructed by calcareous algae (e.g., Dvinella/Donezella, Komia, Cuneiphycus , phylloid algae), Chaeleles sponges, and microbialites, In Japanese seamount reefs, which were located in high-energy open sea settings, rugose corals, tabulate corals, and chaetetids were the important constructors. Steep platform slopes during this time were apparently supported mainly by microbialite and synsedimentary cementation. Upper Upper Carboniferous (Desmoinesian-Virgilian/“Bursumian”, Moscovian-Gzhelian/Orenburgian) tropical shallow-water shelf and shelf-margin carbonate buildups are predominantly bafflestones composed mostly of erect udoteacean phylloid algae. In contemporaneous, slightly deeper-water, mound-flank to intermound areas, communities of calcareous sponges, laminar encrusting red algae, and bryozoans built smaller boundstone reefs. In Lower Permian (Wolfcampian, Asselian-Sakmarian) tropical paleolatitudes, those two buildup communities merged and constructed bafflestone-boundstono reefs in shelf-margin settings that were composed of a framework (baffler guild) of erect phylloid algae, calcareous sponges, and fenestellid and ramose bryozoans, which were encrusted by (binder guild) laminar red algae ( Archaeolithophyllum), Archaeolithoporella, Tuibiphytes , and fistuliporid bryozoans (Chiorosponge association). Many tropical shelf-margin buildups are rich in originally aragonitic botryoidal radial fibrous cements, and in some, heliosponges and specialized Permian reef brachiopods are locally abundant. Such Lower Permian aigal-calcisponge-cement reefs are known throughout the Permian circum-equatorial belt, from present-day southwestern and midcontinent North America, to the circum-Mediterranean region, to southeast and East Asia. That integrated reef-building community radiated and persisted through the rest of Permian time, reaching its acme of development in Middle and Upper Permian tropical reefs, such as the Capitan Reef of the Permian Basin. At more subtropical to warm temperate paleolatitudes, upper Upper Carboniferous to Lower Permian shallow-water shelf to shelf-margin buildups were constructed mainly by Palaeoaplysma , with varying proportions of intermixed phylloid algae, and sometimes botryoidal radial fibrous cements (Chloroforam association). Paleoaplysina buildups are known from around the northern margin of the paleocontinent Laurasia, which includes the present-day northwestern United States, Arctic Canada, the Barents Sea region, and the Russian Ural Mountains region. As seen in Arctic Canada and Russia, contemporaneous, somewhat deeper-water, upper slope buildups were constructed by fenestrate bryozoans and Tubiphytes , and those buildups commonly have pervasive originaily calcitic radiaxial cements tones (Brynoderm to Brynoderm-extended association). The Palaeoaplysina -phylldalgal algal and fenestra tebryozoan-Tubiphytes reef communities intermixed in buildups at intermediate water depths, and the latter buildup type sometimes shallowed upward into the former buildup type. In adjacent deeper-water, lower slope to basinal settings, siliceous sponges constructed organic carbonate buildups (Hyalosponge association) that commonly included intermixed bryozoans and brachiopods at intermediate depths. Most shallow-water, tropical and subtropical buildups were composed predominantly of originally aragonitic organic and inorganic elements (e.g., phylloid algae, Palacoaplysina , calcareous sponges, botryoidal radial fibrous cements), whereas buildups in deeper and/or cooler water were dominated by Mg-calcite constituents (e.g., bryozoans, Tubiphytes , radiaxial cements). Many of the cooler- water biotic elements were also contributors to warm-water reefs, but there they were usually greatly diluted by the more prolific tropical biota.