This text addresses electrothermal problems in modern VLSI systems. Part I, The Building Blocks, discusses electrothermal phenomena and the fundamental building blocks that electrothermal simulation requires (including power analysis, temperature-dependent device modeling, thermal/electrothermal simulation, and experimental setup-calibration). Part II, The Applications, discusses three important applications of VLSI electrothermal analysis including temperature-dependent electromigration diagnosis, cell-level thermal placement and temperature-driven power and timing analysis. This work should be useful for researchers in the fields of IC reliability analysis and physical design, as well as VLSI designers and graduate students.