This　review　provides　an　overview　of　recent　advances　in　hydrothermal　liquefaction　(HTL)　biocrude　production　processes　using　plastics　as　feedstock,　seawater　as　the　processing　medium,　and　microwave　irradiation　as　a　process　intensification　method.　Additionally,　the　review　examines　the　application　of　aid-in　investigation　tools　such　as　kinetics,　machine　learning,　and　feasibility　analysis　to　HTL　research.　All　these　aspects　have　been　underexplored　in　review　literature　compared　to　process　optimization,　biocrude　upgrading,　continuous　HTL,　and　aqueous　phase　reutilization.　The　potential　of　HTL　as　an　effective　method　for　the　depolymerization　of　plastics　is　initially　evaluated.　The　ease　of　plastic　depolymerization　follows　the　order　of　polycarbonate　(300　degrees　C)　＞　polystyrene　(350　degrees　C)　＞　polyethylene　=　polypropylene　(420　degrees　C)　＞　polyethylene　terephthalate　(＞450　degrees　C).　Both　synergism　and　antagonism　are　observed　for　co-HTL　of　plastics　with　biomass,　ranging　from-48.3%　to　79.2%.　Using　seawater　as　an　alternative　HTL　processing　medium　shows　promising　potential,　while　the　effect　of　sea　salts　on　biocrude　yield/　quality　is　still　controversial　especially　when　carbohydrate-rich　feedstocks　are　utilized,　necessitating　more　comprehensive　examination.　Microwave　irradiation　has　been　shown　to　increase　biocrude　yield　from　lipid,　produce　comparable　yields　from　protein　and　lignin,　and　decrease　yield　from　carbohydrate　compared　to　conventional　heating.　As　for　the　aid-in　investigation　tools,　limited　efforts　have　been　made　to　apply　kinetic　modeling　to　the　HTL　of　plastics,　which　could　be　particularly　useful　when　synergism　or　antagonism　is　observed　during　coHTL　of　plastics　and　biomass.　Machine　learning-enabled　predictions　of　product　yield　and　quality　have　been　found　to　be　more　accurate　than　traditional　mathematical　models.　Future　research　could　focus　on　using　machine　learning　algorithms　to　elucidate　product　formation　mechanisms.　The　techno-economic　and　life　cycle　assessment　reveal　that　the　commercialization　of　HTL　technology　remains　a　distant　prospect,　further　improvements　in　product　yield,　quality,　and　process　energy　efficiency　are　essential.　Overall,　this　review　offers　augmented　insights　into　HTL　technology　and　facilitates　the　identification　of　novel　opportunities,　which　is　of　value　to　promote　the　biocrude　production.