The use of plastic has constantly been increasing since the middle of the 20th century. As a consequence, the amount of microplastic in the marine environment worldwide has also risen. Nowadays, plastic more often replaces other materials because of its good qualities. Its negative feature is incomplete degradation, which causes accumulation of big particles in marine environment, as well as small ones (<5 mm) called microplastic. Microplastic in seas has a negative impact on marine biota: it enters the digestive system, causing the accumulated toxins to be transferred through the food chains and eventually end up in humans. Studies demonstrated a positive relationship between microplastic and human population density. There is a need for the standardization of data collecting, which is important for the evaluation of spatial and temporal trends. Additional researches of contaminant bioaccumulation are also necessary. Lately the microplastic issue has been more acknowledged. Still, many questions arise and wait to be solved, especially those connected with the smallest particles called nanoplastics, which are potentially even bigger threat for the environment.