About 10 years ago HERA has opened a new field of studies, namely that of low-x in QCD, initially via structure function measurements, and later with dedicated measurements of the hadronic final state. Theoretical guidance has turned out to be very important for these studies. The hunt for low-x effects in data has been a constant interplay between experiment and theory. This paper gives a personal account of a few examples which are directly related to the work of Jan Kwieciñski and his collaborators.

PACS numbers: 12.38.Qk, 13.60.Hb