A review of the ages determined for mantle material (xenoliths and xenocrysts entrained in kimberlite) derived from the Slave Province continental lithospheric mantle (CLM) indicates that a portion of the central Slave lithosphere may be ancient (3.5–3.3 Ga) harzburgite, but the majority of this lithosphere is much younger (2.9–2.0 Ga). Relying on the most robust chronometers, the majority of Slave lithosphere peridotite formed in the Neoarchean (peak at 2.75 Ga), whereas the majority of eclogite formed in the Paleoproterozoic (2.2–2.0 Ga). The northern Slave lithosphere contains evidence of peridotite xenolith ages that young with depth. The Paleoproterozoic eclogites may have multiple origins including remnants of subducted oceanic crust and mafic–ultramafic magmas that crystallized at great depth (100–200 km). Re–Os studies of sulfide inclusions in diamond indicate that some diamonds currently mined are ancient (∼3.5 Ga), but many Slave diamonds could be considerably younger. Most eclogitic diamonds recovered from the Slave craton are interpreted to be related to the formation of Paleoproterozoic eclogite. There is abundant evidence for Mesoproterozoic modification of the Slave lithosphere (e.g., heating by magma emplacement at great depth and metasomatism) and possible new addition to the lithosphere at that time. The Canadian Slave and African Kaapvaal lithospheres have similar peaks in cratonic peridotite formation ages at about 2.8 Ga, indicating that a large portion of the CLM in these two cratons formed and stabilized in the Neoarchean. One difference is that the Slave peridotites are much less enriched in SiO2, possibly reflecting the more metasomatized nature of the Kaapvaal CLM. The dominance of Paleoproterozoic formation ages for Slave mantle eclogites contrasts with the dominance of Neoarchean formation ages for Kaapvaal mantle eclogites.