The ~3-6Hz theta rhythm has been assigned a crucial role in learning processes, from the first years of life to adulthood. In this talk I will briefly summarize the current state of knowledge and present our recent work on the theta rhythm in early brain development. Most critically, across several studies we found that the theta rhythm is present from the first years of life and involved in the processing of novel and unexpected information. This proposal is in further supported by two of our recent studies. In a first study, we focused on how novel representations are built, by presenting several object stimuli repeatedly, at 6 and 12 months. We found that theta oscillations increase over the first repetitions of a stimulus, but reduced thereafter, and that theta connectivity was higher for unknown stimuli (only shown once), compared to already familiarized stimuli. This indicates that novel information is processes in more extended neural networks, to be integrated over time, when global activity becomes reduced. In a second study we tested the effect of rhythmic stimulation at different frequencies in 9-months-olds and found a resonant phenomenon at 4Hz across a variety of stimulation frequencies, indexing a specific role in perceptual processing in the infant brain. I will discuss these findings in light of the idea that the theta rhythm is an ontogenetically preserved learning mechanism, allowing developing humans to integrate novel information into their developing (semantic) models of the world around them, starting in the infant years.