This chapter looks into how the use of semantic technologies can provide support to common needs in eScience projects, including data-intensive science, facilitating experiment knowledge reuse and recycle among scientists, lowering the barriers of knowledge exchange for interdisciplinary research, and bridging the gap between data from different sources and the gap between data sharing and digital scholarly publication. To illustrate this, we describe a set of pioneering semantic eScience projects that cover a diversity of application domains including bioinformatics, biology, chemistry, physics, environmental science, and astronomy, and we summarize some of the open issues and future lines of research and development in this area.