Plastic pollution in marine ecosystems has become an urgent environmental issue, affecting different marine organisms and their habitats. This chapter reviews the occurrence and effects reported of plastic and microplastic ingestion across marine species, highlighting significant findings from in situ and laboratory studies. Ingestion rates varied significantly among species and conditions; for marine birds, fish, and mammals, ingestion percentages varied widely, with some species recording the absence of microplastics and others reaching 100%. Cephalopods exhibited the highest ingestion rates, ranging from 93% to 100%. Notably, of the articles reviewed, only studies performed under controlled laboratory conditions reported adverse effects, and all reported effects were linked to cellular and internal damage. Mitigation strategies are essential for addressing the increasing problem of marine litter and include regulatory measures, technological innovations, public awareness campaigns, and international collaboration. Effective actions must be taken at local and global levels to protect marine biodiversity and ecosystems from the pervasive threat of plastic pollution. This comprehensive approach aims to reduce plastic waste and its impacts on marine life, emphasizing the need for coordinated efforts in tackling this critical environmental challenge.