This literature review’s main focus discussed how number sense effect students’ mathematical achievement and what strategies teachers can use to build students’ number sense. While researching number sense, it was often found that explicit instruction, teacher knowledge, and socio-economic status impacts students’ knowledge of number sense. It has been found that the earlier students start learning simple math skills the better it will be on their math development as they go into kindergarten and get older. In knowing the importance of number sense, teachers have to know what strategies they should use to support all students build number sense. A common instructional strategy used to teach number sense, is explicit instruction. A few of the many instructional strategies explained in more detail include: Five frames, number lines, think alouds, and concrete to abstract representations. Teachers need to have the knowledge of how strategies can be used to support students’ mathematical understanding. This literature review will also look at instructional strategies, future research, memorizing versus understanding, and the literacy connection of number sense.