Methods and apparatus for safely forming anastomoses comprise magnetic members configured to accommodate different tissue types and patients of differing size and weight. The magnetic members may comprise first and second magnetic members configured to engage each other with a force sufficient to form anastomosis while taking a sufficiently long time to allow the intestinal walls to fuse together. The first and second magnetic members can be configured to form anastomoses between both similar and different types of intestinal tissue. An elongate surgical placement instrument can be configured to engage and manipulate the first and second magnet members through the intestinal wall from outside the intestinal wall in order to place each of the magnetic members at desired locations.