Flexible　and　effective　methods　for　oil–water　separation　are　crucial　for　reducing　pollutant　emissions　and　safeguarding　water　and　fuel　resources.　In　recent　years,　there　has　been　growing　interest　in　fundamental　research　and　engineering　applications　related　to　water　and　fuel　purification,　especially　oil–water　separation.　To　date,　filter　materials　with　special　wetting　characteristics　have　been　widely　used　in　oil–water　separation.　Nanostructured　materials　are　one　of　the　most　attractive　candidates　for　next-generation　oil–water　separation.　This　review　systematically　summarizes　the　mechanisms　and　current　status　of　oil–water　separation　using　nanostructured　materials.　Basically,　this　can　be　achieved　by　using　nanostructured　materials　with　specific　wettability　and　nanostructures.　Here,　we　provide　a　detailed　discussion　of　two　general　approaches　and　their　filtration　mechanisms:　(1)　the　selective　filtration　technique,　based　on　specific　surface　wettability,　which　allows　only　oil　or　water　to　penetrate　while　blocking　impurities;　(2)　the　absorption　technique,　employing　porous　sponges,　fibers,　or　aerogels,　which　selectively　absorbs　impure　oil　or　water　droplets.　Furthermore,　the　main　failure　modes　are　discussed　in　this　review.　The　purposes　of　this　article　are:　(1)　to　summarize　the　methods　of　oil–water　separation　by　nanotechnology;　(2)　to　raise　the　level　of　environmental　protection　consciousness　of　water　pollution　by　using　nanotechnology;　(3)　to　tease　out　the　features　of　different　approaches　and　provide　a　pivotal　theoretical　basis　to　optimize　the　performance　of　filtering　materials.　Several　approaches　for　oil　and　water　separation　are　compared.　Furthermore,　the　principle　and　application　scope　of　each　method　are　introduced.　©　2023　by　the　authors.