Recent experiments withGammasphereand theMicroballcharged‐particle detector array have led to the identification, and have enabled the detailed spectroscopic study, of highly‐deformed and superdeformed rotational bands in a number ofA∼ 40,N≈Znuclei. These rotational bands are built on multi‐particle multi‐hole excitations across theN,Z= 20 shell gap from thesdto thepfshell and, in the context of the Nilsson scheme, are associated with the shell gaps formed at large prolate deformation for particle numbersN,Z= 16, 18, 20 aspf‐shell intruder orbitals are occupied. In analogy with well‐developed rotational motion in heavy nuclei, these highly collective rotational structures involve active valence particles in two major shells for both protons and neutrons, yet theA∼ 40 bands possess the unique advantage that the valence space dimension remains small enough to be approached from a shell‐model perspective. These rotational bands thus provide an ideal opportunity for detailed comparisons between experimental data and both microscopic and macroscopic models of collective motion in nuclei. © 2003 American Institute of Physics