We present a gallery with some of the most interesting microstructures of low-ionization found in planetary nebulae (PNe). A rich zoo of knots, filaments, jets and jet-like systems are introduced, together with their morphological and kinematic properties. We briefly compare the predictions of the theoretical mechanisms for their formation with the observations and find that different physical mechanisms have to be at work. In particular, the following processes seem most promising in explaining these structures: i) in situ dynamical and radiative instabilities, ii) interaction of fossil condensations with the circumstellar medium, iii) HD and MHD collimation produced by disks or by interacting winds, and iv) highly symmetrical mass loss episodes of the progenitor AGB star.