When a male child, who is not a priest or a Levite, is naturally born of his mothers first pregnancy to a mother not descended of Cohanim (Priests) or Levites he must be "redeemed" with the value of five biblical shekels, to be payed to a Cohen (Priest).
- This Mitzvah is based on the pasuk בְּכוֹר בָּנֶיךָ תִּתֶּן לִּי "the firstborn of your sons you shall give Me" and וְכֹל בְּכוֹר אָדָם בְּבָנֶיךָ תִּפְדֶּה "and every firstborn of man among your sons, you shall redeem" . It is considered a Biblical positive commandment. 
- The principle obligation of this law falls on the father. If the father fails to fulfill his obligation, the obligation is transferred to the son to redeem himself when he becomes the age of Bar Mitzvah (13 years old). 
- The mother has no obligation to redeem her son. 
- Regarding bet din's obligation see discussion page
- Shemot 22:28
- Shemot 13:13
- Rambam Sefer HaMitzvot (Aseh #80), S"A Y"D 305:1
- S"A YD 305:15 writes that if the father doesn't redeem his son then the son is obligated to redeem himself when he grows up. The Pitchei Teshuva YD 305:25 quotes the Zichron Yosef who explains that the child should wait until he's the age of Bar Mitzvah so that he is obligated in the Mitzvah himself because as a child he's not obligated in the mitzvah and there's no even Chinuch for it because it's a one time mitzvah.
- S"A YD 305:2