The emergence of new ultrafast optical modulation techniques has opened the way towards a new femtosecond laser technology based on solid-state gain media. This paper addresses the requirements for stable ultrashort pulse generation in these novel femtosecond sources. The theoretical considerations are backed up by experimental results obtained with a number of different laser systems. The conclusions drawn from the presented theoretical and experimental investigations provide general guidelines for the design and optimization of a wide range of femtosecond solid-state laser oscillators.