Lamins are nuclear intermediate filament proteins that form a dense meshwork at the inner face of the inner nuclear membrane in animal cells. Proper assembly of the lamin network is essential to protect nuclei from mechanical stress in mechanically active tissues like striated muscle. Mutations in lamins or lamin binding proteins result in human diseases called laminopathies and often lead to muscular dystrophy and/or dilated cardiomyopathy. Although prior research has begun to uncover the pathological mechanisms behind these diseases, many fundamental functions of lamins remain underexplored. In this dissertation, I present new insights into the evolutionary history of lamins, dissect critical differences between the lamin isoforms found in humans, and deepen our understanding of the interactions between lamins and other nuclear envelope proteins including emerin and lamin B receptor. Using a genetic complementation system, I demonstrate that the abilities of lamins to regulate proper nuclear shape, stiffen nuclei, and maintain nuclear envelope integrity were likely some of the first functions of lamins to evolve in the common ancestor of amoeba and man. I next uncover subtle but important defects imparted by commonly used N-terminal tags fused to Lamin A that impair proper incorporation into the lamina and compromise the ability of nuclei to resist deformation. I then generated a panel of lamin expression constructs including full length lamin isoforms, lamin truncations, and chimeras to elucidate the specific contributions of different lamin protein domains to nuclear stiffness following expression in lamin-deficient cells. This work uncovered key roles of the lamin rod domain for determining the stiffness contributed by each lamin isoform. I additionally identify novel candidate interaction partners of lamins, uncover a previously unappreciated domain of lamin A/C that binds to emerin, and define the additive effects of different lamin protein domains that contribute to the proper localization and anchoring of emerin at the nuclear envelope. Finally, I present work revealing a dynamic interplay between A-type and B-type lamins in the regulation of the subcellular localization of the lamin B receptor. Collectively, these data deepen our understanding of lamins from a basic cell biology perspective and inform what lamin functions may be perturbed in mutant lamins causing disease in humans.