The Mid-oceanic ridges (MORs) provide unique opportunities to study two of the three tectonic plate boundaries: the divergent borders along and across the spreading ridge axis, and the tectonically dominated offset zones (e.g., transform faults). Our understanding of the processes building and modifying the oceanic lithosphere has increased over the past 20 years due to advances in deep-sea research technologies, and analytical and numerical modeling techniques. Increasingly, the processes inferred from the present oceanic lithosphere are also transferred into those operating in the Proterozoic and Archean. Yet, the relative role of magmatic, tectonic, and hydrothermal processes with their interaction in the formation and accretion of the oceanic lithosphere at the ridge, especially at slow and ultra-slow spreading ridges, and along transform faults, remains poorly constrained. Oceanic transform faults and their extension into the fracture zones have previously been considered to be relatively cold and magmatically inactive; however, evidence for magmatism has recently emerged. The complex network of associated faults provides ideal pathways for hydrothermal percolation into the Earth’s lithosphere and may therefore play a significant role in the chemical and the thermal budget of the planet, as well as in the chemical exchange with the ocean (e.g., nutrients). Yet, little is known about fluid circulation in the oceanic lithosphere in these ultra-slow settings. This session objective is to favor scientific exchange across multiple disciplines and to share recent knowledge acquired along mid-oceanic ridge axes and off-axis, besides the oceanic transform faults and their fracture zones. We particularly welcome studies using modern deep-sea high-resolution techniques and ocean lithosphere drilling. The session also welcomes contributions dealing with recent discoveries in hydrothermal systems, and which integrate geophysical, geochemical, petrological and geological data with numerical modeling tools.