The heliosphere inflated by the solar wind in the very local interstellar medium (VLISM) protects the solar system from interstellar charged particles. In contrast, interstellar neutral (ISN) atoms propagate through the heliosphere. Inside the heliosphere, some ISN atoms are ionized by charge exchange, photoionization, and electron impacts, creating a population of pickup ions (PUIs) propagating through the heliosheath. Most PUIs are eventually neutralized and become energetic neutral atoms (ENAs). ISN atoms and ENAs that survive travel to 1 au are detected by dedicated instruments on space missions such as IBEX or IMAP. In the proposed project, we will analyze observations of ISN atoms, PUIs, and ENAs to learn about the structure of the outer heliosphere and the VLISM. We will find how the ISN atoms are modified in the heliospheric boundaries and estimate the physical conditions of the VLISM, which we will interpret in the context of astrophysical observations.