Plastic debris is gradually filling the seas, oceans, and freshwater bodies of the planet. Since the 1950s, a huge amount of plastic has entered into various bodies of water. All these objects decompose at different rates, and aquatic organisms take part in these processes. This book chapter provides an overview of studies carried out in recent decades on the interaction between microorganisms and plastic debris in the aquatic environment. Both prokaryotic communities and algo-bacterial cenoses are considered. A separate section is devoted to the research results of the authors of this book chapter, obtained in the natural environment, contaminated with plastic, and in field experiments in the sea.