Starting from the early research in the 1960s, especially in the last two decades, orthoses and exoskeletons
have been significantly developed. They are designed in different architectures to assist their users’
movements. The research literature has been more prolific on lower-limb devices: a main reason is
that they address a basic but fundamental motion task, walking. Leg exoskeletons are simpler to design,
compared to upper-limb counterparts, but still have particular cognitive and physical requirements from
the emerging human–robot interaction systems. In the state of the art, different control strategies and
approaches can be easily found: it is still a challenge to develop an assistive strategy which makes the
exoskeleton supply efficient and natural assistance. So, this paper aims to provide a systematic overview
of the assistive strategies utilized by active locomotion–augmentation orthoses and exoskeletons. Based
on the literature collected from Web of Science and Scopus, we have studied the main robotic devices
with a focus on the way they are controlled to deliver assistance; the relevant validations are as well
investigated, in particular experimentations with human in the loop. Finally current trends and major
challenges in the development of an assistive strategy are concluded and discussed.