A modular robotic surgical system comprising: a base; a plurality of tool-receivers arranged as separate units, each tool-receiver unit operable to move an elongate surgical tool received therein; a plurality of interface coupling pairs, each coupling pair comprising a first coupler as part of the base and a second coupler as part of each of the tool-receiver units; wherein each of the tool-receiver units is independently and interchangeably attachable to the base via the coupling pair.