The introduction of molecular methods has facilitated the investigation of physiology, ecology, and distribution of phytoplankton species, especially of those that are missing distinct morphological features. Previous publications have shown the power of the analysis of ribosomal genes (rRNA-genes) to gain new insights into the phylogeny, for taxonomical identification or the community structure of both prokaryotic and eukaryotic micro organisms.This course is dedicated to introduce you to relevant basics and methodologies related to the assessment of marine molecular ecology. In particular, the course is designed to demonstrate the basics of PCR-based approaches, and the potential and advantages of the analysis of rRNA-genes for the assessment of marine phytoplankton biodiversity.