This conference brings together a wide variety of mathematical methods with defence and security applications. The programme will include keynote speakers, presentations and poster sessions, as well as refreshment breaks for informal discussions. It is aimed towards mathematicians, scientists and engineers from both industry and academia, in addition to government and military personnel who have an interest in how mathematics can be applied to defence and security problems. This will be the sixth Mathematics in Defence and Security, conference albeit the first with ‘Security’ explicitly mentioned in the title; the previous conferences each attracted over 100 delegates from a wide range of organisations including Dstl, QinetiQ, AWE, BAE Systems, Thales, Rolls Royce, the IMA, the MoD, academia and international parties. In response to the Covid-19 situation, this event will be held virtually via Zoom Webinar. Our intention is that the scientific programme will remain very similar to that of an in-person event. This year we are delighted that keynote presentations will be given by Dr Ned Allen (Former Lockheed Martin Chief Scientist), Phillippa Spencer (DSTL) and Marc Widdowson (Director of Amarna Ltd)