Marine biofouling remains an unresolved problem with serious economic impact for different industries. Marine biofilms are the initial step of the marine fouling process in artificial surfaces and are the preferential substrata for the settlement of macroinvertebrate larvae and macroalgae spores. In this thesis, an extensive and critical literature review was carried out to digest current information on the distribution of marine biofilms, the already known chemical cues involved in their formation, as well the overall importance of marine biofilms for the marine fouling process. In addition, to understand how the marine biofilm formation process evolves, we employed amplicon-based NGS (Next-generation sequencing) methodologies to characterize early-stage marine biofilms growing on steel surfaces in two distinct seasons in the port of Leixões in Northern Portugal. The 16S rRNA gene sequencing data analysis demonstrated distinct taxonomic and functional profiles of the marine biofilm communities in the sampled seasons, suggesting that seasonality is a major factor influencing the diversity of those prokaryotic communities. Furthermore, the sampled biofilms revealed the presence of pathogenic taxa which, accordingly to our knowledge was not reported previously, and whose abundance was significantly influenced by temporal variations. This knowledge should be important for future anti-fouling and anti-corrosion purposes. After years of application of toxic antifoulants to control biofouling, there is a strong necessity for the development of environmentally friendly antifouling products, and cyanobacteria are a particularly encouraging source of new natural antifouling compounds. An extensive screening was therefore performed with crude organic extracts of 61 cyanobacterial strains of the LEGE Culture Collection (LEGE CC) to test their anti-fouling potential. The obtained fractions of several cyanobacterial strains revealed significant activity against the growth of microfouling organisms involved in marine biofilm formation (bacteria and diatoms) and inhibited the quorum-sensing (QS) phenomenon, which is associated with biofilm formation. Subsequent work resulted in a set of HPLC-PDA purified bioactive fractions from a marine cyanobacterial strain whose structure is being elucidated by spectroscopic methods.