1. General Introduction 2. The Notch Pathway 3. Wnt Signaling 4. The RANK-L/LGR4 Loop 5. The Sphingosine Pathway 6. Nuclear Receptors 7. Epigenetic Regulation of Bone and Bone Cells 8. The Brain-Bone Connection 9. Pituitary-Bone Axis 10. Muscle-Bone Interactions 11. Bone and Fat 12. Bone and Energy Homeostasis 13. Hematopoietic niches, Blood Cells and Skeletal Homeostasis 14. Bone and the Vasculature 15. Osseous-Immune Interactions