Simple　Summary　This　review　highlights　the　intricate　interactions　between　two　major　constituents　of　marine　ecosystems:　dinoflagellates　and　heterotrophic　bacteria.　Dinoflagellates　typically　associate　with　a　diverse　array　of　heterotrophic　bacteria,　which　are　not　limited　to　but　predominantly　consist　of　phyla　such　as　Alphaproteobacteria,　Gammaproteobacteria,　and　the　Cytophaga-Flavobacterium-Bacteroides　group.　These　bacterial　communities　engage　with　dinoflagellates　in　a　multifaceted　manner,　including　nutrient　exchange,　the　secretion　of　pathogenic　substances,　and　involvement　in　the　synthesis　of　chemical　entities.　Crucially,　the　process　of　horizontal　gene　transfer　from　bacteria　is　a　significant　force　sculpting　the　genomic　architecture　of　dinoflagellates.　The　objective　of　this　review　is　to　shed　light　on　the　dynamic　interactions　between　dinoflagellates　and　their　bacterial　partners,　examining　the　relationship　through　a　physiological,　ecological,　and　evolutionary　perspective.Abstract　Dinoflagellates　and　heterotrophic　bacteria　are　two　major　micro-organism　groups　within　marine　ecosystems.　Their　coexistence　has　led　to　a　co-evolutionary　relationship　characterized　by　intricate　interactions　that　not　only　alter　their　individual　behaviors　but　also　exert　a　significant　influence　on　the　broader　biogeochemical　cycles.　Our　review　commenced　with　an　analysis　of　bacterial　populations,　both　free-living　and　adherent　to　dinoflagellate　surfaces.　Members　of　Alphaproteobacteria,　Gammaproteobacteria,　and　the　Cytophaga-Flavobacterium-Bacteroides　group　are　repeatedly　found　to　be　associated　with　dinoflagellates,　with　representation　by　relatively　few　genera,　such　as　Methylophaga,　Marinobacter,　and　Alteromonas.　These　bacterial　taxa　engage　with　dinoflagellates　in　a　limited　capacity,　involving　nutrient　exchange,　the　secretion　of　pathogenic　substances,　or　participation　in　chemical　production.　Furthermore,　the　genomic　evolution　of　dinoflagellates　has　been　profoundly　impacted　by　the　horizontal　gene　transfer　from　bacteria.　The　integration　of　bacterial　genes　into　dinoflagellates　has　been　instrumental　in　defining　their　biological　characteristics　and　nutritional　strategies.　This　review　aims　to　elucidate　the　nuanced　interactions　between　dinoflagellates　and　their　associated　bacteria,　offering　a　detailed　perspective　on　their　complex　relationship.