In　this　article,　we　present　the　notion　of　«mobile　3C　systems»　in　which　communications,　computing,　and　caching　(i.e.,　3C)　make　up　the　three　primary　resources/functionalities,　akin　to　the　three　primary　colors,　of　a　mobile　system.　We　argue　that　in　future　mobile　networks,　the　roles　of　computing　and　caching　are　as　intrinsic　and　essential　as　communications,　and　only　the　collective　usage　of　these　three　primary　resources　can　support　the　sustainable　growth　of　mobile　systems.　By　defining　the　3C　resources　in　their　canonical　forms,　we　reveal　the　important　fact　that　caching　affects　the　mobile　system　performance　by　introducing　non-causality　into　the　system,　whereas　computing　achieves　capacity　gains　by　performing　logical　operations　across　mobile　system　entities.　Many　existing　capacity-enhancing　techniques　such　as　coded　multicast,　collaborative　transmissions,　and　proactive　content　pushing　can　be　cast　in　the　native　3C　framework　for　analytical　tractability.　We　further　illustrate　the　mobile　3C　concepts　with　practical　examples,　including　a　system　on　broadcast-unicast　convergence　for　massive　media　content　delivery.　The　mobile　3C　design　paradigm　opens　up　new　possibilities　as　well　as　key　research　problems　bearing　academic　and　practical　significance.　©　2016　IEEE.