Grayanoids, occurring exclusively in Ericaceae plants, are well-known highly toxic components from the genera Rhododendron, Pieris, Leucothoe, Craibiodendron, Lyonia, Kalmia, etc. Grayanoids have been the topic of research in many phytochemical and pharmacological laboratories due to their complex structures and fascinating bioactivities. This review, citing 100 references, summarises their chemistry, including the total synthesis and bioactivity of grayanoids isolated from the Ericaceae family in the last five decades, to illustrate the chemo-diversity and biological significance of these diterpenoids.