It depends on the product. We didn't have many resources when I was writing code for barcode readers so we had an informal arrangement whereby one person wrote

It depends on the product. We didn't have many resources when I was writing code for barcode readers so we had an informal arrangement whereby one person wrote the code and two people reviewed it. For my mobile (cell phone) base station code, we had formal review meetings with the programming team, project manager and, when he had time, the VP of R&D. The most strict of all was when I was writing code for an air traffic control system. Every single line of my code was reviewed a minimum of three times. We spent almost as much time reviewing the code as we did writing it.