Hydrogen　energy　serves　as　an　ideal　alternative　energy　carrier　to　fossil　fuels　in　the　future　clean　energy　system.　The　hydrogen　evolution　reaction　(HER)　occurring　at　the　cathode　of　water　electrocatalysis　has　been　considered　as　a　promising　approach　to　produce　hydrogen　over　the　past　decades　due　to　zero　carbon　emission.　To　gain　a　deep　insight　into　the　advanced　electrocatalyst,　herein,　we　provide　a　comprehensive　review　with　an　emphasis　on　the　recent　state-of-the-art　advances　of　HER　electrocatalysts　in　view　of　controlling　their　local　electronic　structure,　creating　defect　nanostructures,　exposing　active　sites,　altering　d　band　center,　and　constructing　heterogeneous　structure.　Initially,　we　start　with　a　brief　introduction　of　the　fundamental　electrocatalytic　mechanisms　and　the　critical　electrochemical　parameters　for　evaluating　HER.　Then,　we　systemically　discuss　three　representative　classes　of　electrocatalysts,　comprised　of　highly　active　noble-metal　including　single　atom,　nanoparticles,　and　clusters,　earth-abundant　transition　metal　such　as　transition　metal　sulfides,　phosphides,　carbides,　nitrides,　and　oxides,　and　metal-free　functional　nanomaterials　involving　different　dimensions　of　carbonaceous　nanomaterials,　boron　nitrogen,　and　phosphorous　non-carbonaceous　nanomaterials　by　adjusting　their　tunable　electronic　structures　and　architectures/morphologies　with　a　particular　emphasis　on　the　structure-function　relationships.　Finally,　we　point　out　the　current　challenges　and　opportunities　in　view　of　achieving　highly　active　and　stable　electrocatalysts　towards　practical　applications.