This chapter addresses the stopping and straggling of ions at velocities up to the Thomas-Fermi speed vTF = Z1 2/3v0, with the main focus on velocities up to the Bohr speed v0.This topic is characterized by many unsolved problems both on the experimental and the theoretical side. Experimental findings play a more dominant role in this chapter than in other parts of this monograph. The newly found reciprocity principle is explored in the evaluation of data. Much existing theory is based directly or indirectly on electron-gas theory, especially Fermi-gas theory. The Lindhard-Scharff formula and Firsov’s theory are discussed along with various extensions. The transport cross section approach is explored in conjunction with partial waves, Born approximation as well as linear and nonlinear dielectric theory. Stopping cross sections are known to show pronounced oscillations as a function of the atomic number Z1 of the projectile, and presumably also of Z2, where evidence is weaker.