In Chapter 2, I focus on the acquisition of number concepts related to natural numbers. I review nativist views, as well as Dehaene’s early view that number concepts arise from estimations due to the approximate numbers system. I end up focusing in most detail on the bootstrapping account of Carey and Beck, according to which the object tracking system is the key cognitive resource used in number concept acquisition. However, I endorse a hybrid account that also includes an important role for the approximate numerosity system. I then review some of the criticism against the bootstrapping account, concluding that, while more empirical data is needed to establish its correctness and details, currently it provides the most plausible account of early number concept acquisition.