For decades, cell lines have played a critical role in scientific developments. In most cases, researchers just got data generated from cell lines. However, due to some weaknesses of cell lines, scientists become increasingly cautious about these generated results. But now the game has changed! Primary cells now are believed to be a more biologically relevant tool than cell lines for studying human and animal biology. And we design this primary cell culture guide aimed at showing new investigators the basic principles of primary cell and some practical culture skills.