Contentless experience involves an absence of mental content such as thought, perception, and mental imagery. In academic work it has been classically treated as including states like those aimed for in Shamatha, Transcendental, and Stillness Meditation. We have used evidence synthesis to select and review 135 expert texts from within the three traditions. In this paper we identify the features of contentless experience referred to in the expert texts and determine whether the experiences are the same or different across the (...) practices with respect to each feature. We identify 65 features reported or implied in one or more practices, with most being reported or implied in all three. While there are broad similarities in the experiences across the traditions, we find that there are differences with respect to four features and possibly many others. The main difference identified is that Shamatha involves substantially greater attentional stability and vividness. Another key finding is that numerous forms of content are present in the experiences, including wakefulness, naturalness, calm, bliss/joy, and freedom. The findings indicate that meditation experiences described as contentless in the academic literature can in fact involve considerable variation, and that in many and perhaps most cases these experiences are not truly contentless. This challenges classical understandings in academic research that in these so-called contentless experiences all content is absent, and that the experiences are therefore an identical state of _pure consciousness_ or consciousness itself. Our assessment is that it remains an open question whether the experiences aimed for in the three practices should be classed as pure consciousness. Implications of our analysis for neuroscientific and clinical studies and for basic understandings of the practices are discussed. (shrink)