Acid　catalysts　are　widely　used　in　petrochemical　reactions,　the　synthesis　of　fine　chemicals,　and　biomass　conversions　in　industry.　To　comply　with　the　principles　of　green　and　sustainable　chemistry,　much　attention　is　being　paid　to　the　replacement　of　traditional　liquid　acids　with　solid　acid　catalysts.　Normally,　solid　acids　exhibit　hydrophilicity　because　of　the　unique　hydrophilic　nature　of　the　acidic　sites　on　their　surfaces.　Water,　as　a　typical　solvent,　byproduct,　or　negative　component　in　a　variety　of　acid-catalyzed　reactions,　may　be　adsorbed　on　solid　acids　and　then　cause　the　deactivation　of　catalytic　sites　or　hydrolysis　of　the　frameworks.　The　development　of　solid　acids　with　suitable　hydrophobicity　largely　overcomes　these　issues　and　enhances　their　catalytic　activities　and　reusability.　This　Review　discusses　some　recent　advances　in　the　preparation　of　novel　solid　acids　with　controllable　wettability　and　suitable　hydrophobicity　and　highlights　their　application　in　catalyzing　various　reactions　such　as　esterification,　transesterification,　acylation,　condensation,　hydration,　and　depolymerization　of　crystalline　cellulose.　In　addition,　this　Review　discusses　how　the　hydrophobicity　of　solid　acids　is　affected　by　their　structures,　surface　characteristics,　and　acid　centers,　and　determines　the　principles　for　designing　solid　acids　with　high　catalytic　activity　and　good　reusability.　It　is　instructive　for　researchers　who　are　interested　in　designing　new　kinds　of　solid　acids　with　improved　efficiency　and　reusability　for　applications　in　green　and　sustainable　chemistry.　©　2017　American　Chemical　Society.