Suppose that f Zn>1 an(f)qTn is a cusp form of weight 2k (k E N). We denote by L(f, s) the L-function of f. For Re(s) sufficiently large, the value of L(f, s) is given by L(f, s) = En>1 an), and one can show that L(f, s) has analytic continuation to the entire complex plane. The value of L(f, s) at s = k will be of particular interest to us, and we will refer to this value as the central critical value of L(f, s). Let XD denote the Dirichlet character associated to the extension Q(\D)/Q, that is, XD (n) (va), where AD denotes the discriminant of Q( D)/Q. Define the Dth quadratic twist of f to be fxD = En>1 an(f)XD (n)qn. For any integer D, the L-function of fx, is the Dth quadratic twist of L(f, s), that is, L(fxD , s) Zn> aan(f )XD(n). We will be interested in determining how often L(fxD,s) has nonzero central critical value as D varies over all integers. Since XD 2 = XD we will restrict our attention to the square-free integers D. We expect that as we let D vary over all of the square-free integers, a positive proportion of the L-functions L(fxD , s) will have nonzero central critical value. Indeed, Goldfeld [7] conjectures that for newforms f of weight 2, L(fxD 1) 78 0 for 1 of the square-free integers. Given an elliptic curve E: y2 = x3 +Ax2 +Bx+C (A, B, C E Z) with conductor NE and an integer D, we define the Dth quadratic twist of E to be the curve ED: Y2 = x3+ADx2+BD2x+CD3. Let L(ED, s) denote the L-function associated to ED. For square-free D coprime to 2NE, L(ED, s) is simply the Dth quadratic twist of L(Ei, s). If f E S2(N) is a newform with integer coefEcients, we know via the theory of Eichler and Shimura that there is an elliptic curve E over Q having conductor N so that L(E, s) = L(f, s). Thus if D is coprime to 2N, then L(ED, s) L(fXD, s). Also, one knows from the work of Kolyvagin [13], as supplemented by the work of Murty and Murty [17] or that of Bump, Friedberg and Hoffstein [3] (see also [10] for a shorter proof), that if E is a modular elliptic curve and if L(E, 1) 7 0, then the rank of E is 0. Thus, if f has the property that a positive proportion of the twists of L(f, s) have nonzero central critical value, then this implies that a positive density of the quadratic twists ED have rank 0. There have been many papers which have proved results in this direction. For example, in [2], [3], [6], [10], [16], [17], [19], [28] one can find general theorems on