 Courses since 1980. For instance, one can refer to the 1998 issue of this series, especially "Basic Mechanisms for the New Millenium" by Paul V. Dressendorfer, which recalls much of the physics involved in radiation effects [Dres-98]. Consequently, we shall not address in detail all the work done by generations of experts these last 40 years, as thorough treatments of this rich and still mysterious subject have been done. The objective of this chapter is therefore only to give a review on the subject of total dose modeling with emphasis on analytical and numerical schemes as developed now. We shall also only introduce the debatable issues of interface states, bipolar transistors and prediction and specification in a time-dependent radiation environment. As leakage currents in MOS technologies are a major concern for the range of dose considered, we shall focus on modeling of the oxide trapped charge, especially in medium-to-thick oxides, and describe situations in field oxides of bulk CMOS and buried oxides in SOI. For that purpose, we shall follow a natural roadmap, starting from basics to go on with analytical equations and modeling, and finally use computer codes, lab-made or commercially available. 2. CONTEXT: TOTAL-DOSE ENVIRONMENT IN SPACE 2.1. RECALLING THE ORDER OF MAGNITUDE OF RADIATION IN SPACE Two types of particles can be encountered by space vehicles and interact inside components in spite of shields: A pervasive component that comes directly from outer space (Sun, our galaxy, foreign galaxies). Another component that resides in magnetic fields of the Van Allen Belts and impacts the spacecraft orbiting in them or crossing them. The components of these fluxes have been extensively studied and are recalled of fig. 1. The reader can refer for further description to recent Short Courses of this collection [Barth-97], [Dyer-98]. III-4 a) Trapped-electron Geomagnetic b) Trapped-proton Geomagnetic cm 2s cm-2s- 2x106 3x106 (Earth radii) (Earth radii) Figure 1. Radiation environment and particle densities cl