Some embodiments include an integrated assembly having a source structure. The source structure includes, in ascending order, a first conductively-doped semiconductor material, one or more first insulative layers, a second conductively-doped semiconductor material, one or more second insulative layers, and a third conductively-doped semiconductor material. The source structure includes blocks extending through the second conductively-doped semiconductor material. Conductive levels are over the source structure. Channel material extends vertically along the conductive levels, and extends into the source structure to be in direct contact with the second conductively-doped semiconductor material. One or more memory cell materials are between the channel material and the conductive levels. Some embodiments include methods of forming integrated assemblies.