The estimation of a microalgal population size is no easy task due to the microscopic size of the cells. Consequently, it is impossible to physically count them with the naked eye. The size of microalgae falls within the size of other microbes (e.g., bacteria) and, as a result, most of the methods used for microbial cell counting are also applicable to microalgae. In general, conventional microbiological protocols are available and are sufcient for cell enumeration despite the proliferation of modern and advanced techniques. It is recommended that the researcher choose a method after assessing the costs involved because some of the latest methods require very sophisticated and expensive equipment.