Space Weather in the form of geomagnetic storms and solar energetic particle events (SEPs) drives changes in the near-Earth radiation environment. This environment consists of several types of high-energy charged particles: electrons and protons trapped by the Earth's magnetic field in the Van Allen radiation belts; protons and heavy ions coming directly from solar flares (SEPs); and heavy ions coming from cosmic rays (extra-solar sources.) The trapped-particle Van-Allen belts consist of inner and outer bands. The inner band population contains both electrons and protons and is relatively stable. The outer band population contains primarily electrons, is relatively dynamic and highly responsive to Space Weather effects. Cosmic ray fluxes, on the other hand, are modulated by general solar activity on timescales of the solar cycle. All of these particles interact destructively with satellite surfaces, internal instrumentation, and humans in space, causing a variety of harmful effects. The most severe of these effects include surface charging and arcing, deep dielectric charging and discharging, single-event upsets, and cumulative dose accumulation. Most of these processes affect electronic components on satellites and other spacecraft, however cumulative dose also adversely affects humans in space and is one of the primary safety concerns for manned spaceflight. A precise knowledge of these “Space Environment Effects” (SEE), their expected severity, occurrence rates, and cumulative effect, is essential for satellite design, mission planning, and mission operations. The first step in developing this knowledge is to obtain an accurate picture of the near-Earth radiation environment and this is done primarily through numerical modeling of that environment, supported by any available in-situ data sources. Here, a descriptive overview of the near-Earth radiation environment will be given, followed by a discussion of the interplay of the environment with satellite instrumentation, and a brief synopsis of the current 'state-of-the-art' in radiation environment modeling.