Observations and theory of cataclysmic variables: On progress and problems in understanding dwarf novae and nova-like stars

After brief historical and theoretical introductions to the field, observed properties of dwarf novae and non-magnetic nova-like stars are reviewed. Photometric observations splitted into events on time-scales of months to years (outburst light curves), hours (orbital light curves) and minutes and below (flickering and oscillations), respectively, and spectroscopic observations are presented. The emphasis is on one hand on the features common to many objects in an attempt to gain some impression on what could be considered typical features. On the other hand observations are highlighted that spectacularly deviate from these common trends as they may give some hint as to what the possible range of variability is. Whenever possible, the implications for the physical properties and possible models of the systems are pointed out. Furthermore, for each section the current status of the conceptual understanding and attempts to model this are briefly reviewed and, finally, confronted with the observations.