The Conway Polynomial (or Alexander-Conway polynomial) ΔL(z) of an oriented knot or link L is given by det(z1/2A - z-1/2At), where A is a Seifert matrix for L.
It can be shown that the Conway Polynomial is determined by the following skein relations:
(1) ΔUnknot(z) = 1
(2) ΔL+(z) - ΔL-(z) = zΔL0(z),
where L+, L-, and L0 are three oriented links which are the same except in a neighborhood of a point where they differ as in the figure below.
 Lickorish, W. B. R., An introduction to knot theory. New York: Springer (1997).
 Image taken from Wikipedia, Alexander Polynomial.