November this year will see the fourth edition of the workshop on “Advanced RF Sensors and Remote Sensing Instruments” (ARSI '14) organized by ESA/ESTEC. As in previous years, the purpose is to bring together experts from industry and research organizations to share and present their latest findings on RF remote sensing technology, processing and systems. In addition this year, ARSI’14 is organised jointly with the second edition of the “Ka-band Earth Observation Radar Missions” (KEO’14), considering the interest showed in the first edition in Nov. 2012. This workshop has a similar character to ARSI but concentrates entirely on all aspects relating to Ka-band Earth Observation instruments. The objectives of the two combined workshops are to review the state of the art in current and future mission concepts including applications, science objectives, mission design and instrument technology. This includes new ideas for applications enabled by Ka-band SAR and InSAR. The combined event will take place from 4-7 November 2014 at ESTEC, Noordwijk, The Netherlands. Industry, Researchers and Engineers active in the field are cordially invited to participate and to present their latest findings.