The Interstellar Boundary Explorer (IBEX) is one of five Small Explorer (SMEX) missions undergoing Phase A study for NASA’s Office of Space Science. Around November 2004, NASA expects to select at least one of missions for development and flight. If selected, IBEX will provide the first global views of the Sun’s interstellar boundaries by taking a set of global energetic neutral atom (ENA) images at a variety of energies. Recent advances in ENA imaging have made it possible to remotely image space plasmas and ENA imaging is now poised to image the interstellar interactions and interstellar boundaries at the edge of our heliosphere. IBEX makes these exploratory ENA observations using two ultra‐high sensitivity ENA cameras on a simple spinning spacecraft. IBEX’s highly elliptical Earth orbit allows viewing of the outer heliosphere from beyond the Earth’s relatively bright magnetospheric ENA emissions. IBEX’s sole, focused science objective is to discover the global interaction between the solar wind and the interstellar medium. IBEX achieves this objective by answering four fundamental science questions: (1) What is the global strength and structure of the termination shock? (2) How are energetic protons accelerated at the termination shock? (3) What are the global properties of the solar wind flow beyond the termination shock and in the heliotail? and (4) How does the interstellar flow interact with the heliosphere beyond the heliopause? The IBEX objective is central to the Sun‐Earth Connection (SEC) theme as demonstrated by both the 2003 SEC Roadmap and 2002 NRC’s Decadal Survey and is specifically identified in the 2003 NASA‐wide Strategic Plan. In short, the IBEX mission provides the first global views of the Sun’s interstellar boundaries, unveiling the physics of the heliosphere’s interstellar interaction, providing a deeper understanding of the heliosphere and thereby astrospheres throughout the galaxy, and creating the opportunity to make even greater unanticipated discoveries. © 2004 American Institute of Physics