Abstract: I will discuss my lab efforts in identifying quantitative principles that underlie how tissues grow back to their appropriate size and shape following an amputation or injury. Using zebrafish appendages as model systems, I will describe how traveling waves and scaling gradients of activity of the Fgf/Erk pathway control osteoblast regeneration in bones of different sizes and shapes. I will also discuss how fibroblast regeneration is controlled by a mechanism ensuring proper spatial organization of proliferating cells.