The second knot polynomial discovered. Unlike the firstdiscovered Alexander polynomial, the Jones polynomial can sometimes distinguish handedness (as can its more powerful generalization, the HOMFLY polynomial). Jones polynomials are Laurent polynomials in assigned to an knot. The Jones polynomials are denoted for links, for knots, and normalized so that
(1)

For example, the righthand and lefthand trefoil knots have polynomials
(2)
 
(3)

respectively.
If a link has an odd number of components, then is a Laurent polynomial over the integers; if the number of components is even, is times a Laurent polynomial. The Jones polynomial of a knot sum satisfies
(4)

The skein relationship for under and overcrossings is
(5)

Combined with the link sum relationship, this allows Jones polynomials to be built up from simple knots and links to more complicated ones.
Some interesting identities from Jones (1985) follow. For any link ,
(6)

where is the Alexander polynomial, and
(7)

where is the number of components of . For any knot ,
(8)

and
(9)

Let denote the mirror image of a knot . Then
(10)

Jones defined a simplified trace invariant for knots by
(11)

The Arf invariant of is given by
(12)

(Jones 1985), where i is . A table of the polynomials is given by Jones (1985) for knots of up to eight crossings, and by Jones (1987) for knots of up to 10 crossings. (Note that in these papers, an additional polynomial which Jones calls is also tabulated, but it is not the conventionally defined Jones polynomial.)
Jones polynomials were subsequently generalized to the twovariable HOMFLY polynomials, the relationship being
(13)

(14)

They are related to the Kauffman polynomial F by
(15)

Jones (1987) gives a table of braid words and polynomials for knots up to 10 crossings. Jones polynomials for knots up to nine crossings are given in Adams (1994) and for oriented links up to nine crossings by Doll and Hoste (1991). All prime knots with 9 or fewer crossings have distinct Jones polynomials. However, there exist distinct knots (and even knots having different crossing numbers) that share the same Jones polynomial. Examples include (05001, 10132), (08008, 10129), (08016, 10156), (10025, 10056), (10022, 10035), (10041, 10094), (10043, 10091), (10059, 10106), (10060, 10083), (10071, 10104), (10073, 10086), (10081, 10109), and (10137, 10155) (Jones 1987). (Incidentally, the first four of these also have the same HOMFLY polynomial.)
It is not known if there is a nontrivial knot with Jones polynomial 1.
The Jones polynomial of an torus knot is
(16)

Let be one component of an oriented link . Now form a new oriented link by reversing the orientation of . Then
(17)

where is the Jones polynomial and is the linking number of and . No such result is known for HOMFLY polynomials (Lickorish and Millett 1988).
Birman and Lin (1993) showed that substituting the power series for as the variable in the Jones polynomial yields a power series whose coefficients are Vassiliev invariants.
Let be an oriented connected link projection of crossings, then
(18)

with equality if is alternating and has no reducible crossing (Lickorish and Millett 1988).
Witten (1989) gave a heuristic definition in terms of a topological quantum field theory, and Sawin (1996) showed that the "quantum group" gives rise to the Jones polynomial.