In this PhD thesis, a novel experimental technique has been implemented to study the variables controlling the undulatory locomotion of a tiny worm. Well known for its elegant slithering motion and simple biology, the millimetre-sized nematode Caenorhabditis elegans was chosen to serve as a model organism for our work. The emphasis of this thesis, as embodied by three separate research projects, has been to study the passive and active biomechanical properties of C. elegans, as well as to investigate inter-worm interactions. Micropipette deflection has been used to directly probe forces in a time-resolved manner and with high dynamic resolution. The viscoelastic material properties of C. elegans were explored on a biologically and structurally relevant length scale, and the elastic properties of the body were quantified. Furthermore, the soft tissue was found to behave as a shear-thinning fluid: a non-Newtonian property that has interesting implications on the undulatory locomotion strategy of the nematode. Micropipette deflection furthermore allowed for measurements of the active swimming dynamics of C. elegans. Our experiments quantified the drag coefficients of the tiny worm as well as the viscous forces present in its swimming motion. Swimming experiments were performed in a normal buffer solution, in the confinement of solid boundaries, as well as in fluids with increased viscosities, and the dynamics of the gait modulating worm was investigated. Finally, the binary interactions between two swimming nematodes were studied, utilizing the high micromechanical control provided by the micropipette-based technique. Our findings provide new insight into the physics of undulatory locomotion and active materials in general. / Thesis / Doctor of Philosophy (PhD)