An overview of the characteristics of short-term light variability on T Tauri stars is given. The evidence of the occurrence of flares comes from observations mainly at X-ray energies and from patrole observations in the ultraviolet spectral region. From such observations some limits on the peak fluxes and total energies of the largest flare-like events can be set. In addition, the frequency of such events can be deduced for a number of stars. It is demonstrated that there appears to be a qualitative difference between powerful flare-like events on the weak-line T Tauri stars (NTTs) and those on strong-line stars (CTTs). While it appears that the concept of surface flares occurring on NTTs may be correct there is the evidence that the disk-stars in addition produce flare-like events of a different nature. These events could be related to processes occurring not on the stars but in their circumstellar environment, for instance in a circumstellar disk. We also point at observations that could be of importance in clarifying the cause of flare-like activity on T Tauri stars and also comment on how this activity changes with stellar age.