To　quantify　the　risk　of　the　transmission　of　respiratory　infections　in　indoor　environments,　we　systematically　assessed　exposure　to　talking-and　breathing-generated　respiratory　droplets　in　a　generic　indoor　environment　using　computational　fluid　dynamic　(CFD)　simulations.　The　flow　field　in　the　indoor　environment　was　obtained　with　SST　k-omega　model　and　Lagrangian　method　was　used　to　predict　droplet　trajectories,　where　droplet　evaporation　was　considered.　Droplets　can　be　categorized　into　small　droplets　(initial　size　＜=　30　mu　m　or　＜=　10　mu　m　as　droplet　nuclei),　medium　droplets　(30-80　mu　m)　and　large　droplets　(＞100　mu　m)　according　to　the　exposure　characteristics.　Droplets　up　to　100　mu　m,　particular　the　small　ones,　can　contribute　to　both　short-range　and　long-range　airborne　routes.　For　the　face-to-face　talking　scenario,　the　intake　fraction　and　deposition　fractions　of　droplets　on　the　face　and　facial　mucosa　of　the　susceptible　were　up　to　4.96%,　2.14%,　and　0.12%,　respectively,　indicating　inhalation　is　the　dominant　route.　The　exposure　risk　from　a　talking　infector　decreases　monotonically　with　the　interpersonal　dis-tance,　while　that　of　nasal-breathing　generated　droplets　maintains　a　relatively　stable　level　within　1.0　m.　Keeping　an　angle　of　15　degrees　or　above　with　the　expiratory　flow　is　efficient　to　reduce　intake　fractions　to　＜0.37%　for　small　droplets.　Adjusting　the　orientation　from　face-to-face　to　face-to-back　can　reduce　exposure　to　small　droplets　by　approximately　88.0%　during　talking　and　66.2%　during　breathing.　A　higher　ventilation　rate　can　reduce　the　risk　of　exposure　to　small　droplets　but　may　increase　the　risk　of　transmission　via　medium　droplets　by　enhancing　their　evaporation　rate.　This　study　would　serve　as　a　fundamental　research　for　epidemiologist,　healthcare　workers　and　the　public　in　the　purpose　of　infection　control.