Algae are autotrophic organisms and thallophytes are the main component of plankton and marine benthos. It is the group most affected by climate change variations when performing photosynthesis and is the main base of the food chain in the ocean and world. This book is developed in 3 chapters: Chapter 1 Phycology. the background is described, where it is mentioned that there are few phycofloristic studies and inventories in the State of Campeche compared to the rest of the Mexican coast and given the great diversity of algae in the tropics due to its vast morphology, size and cellular structure, color are key to recognition, thus derives the problem of addressing with this guide to identify the algae of Sabancuy, Campeche Mexico. In Chapter 2 Methodology for the Collection and Recognition of Algae. It is proposed where and how the collection was carried out, which was established at the limit of a 60 m transect perpendicular to the coastline parallel to it by using GPS to register the place, the collections were carried out by means of basic snorkeling for the entire quadrant. The basic elements to make a quick and assertive identification. Using color, size, external morphological structures such as type of thallus and branching, frond, apex structure, phyllodes, stolon, rhizoids, formade, reproduction structures, flotation structures, among others. In Chapter 3 Morphology and Species Recognition. The images of algae collected annually in the period 2006 to 2018 and 2022 are presented. Likewise, a phycofloristic list of 42 species distributed in three divisions is presented: Chlorophyta (16 species and 9 genera), in Rhodophyta (21 species and 15 genera) and in the Division Heterokontophyta (5 species and 4 Genera). For each division, it is described from the morphology and the external characteristics of the collected specimens were considered for recognition and references for the elaboration of a guide and the identification of algae for the area. The description of the morphology of the algae was supported by authors with a recognized trajectory in the field.