A new method for constructing J-R curves is presented, which directly generates the J-Δa relation in a closed, analytical form. This new method makes use of the Concise Format and the Common Format, both developed by Donoso and Landes. These formats relate load, P, to ligament length, b, and displacement — in the elastic and in the plastic deformation ranges, respectively — and have proved useful in calculations in fracture mechanics. Key to the method is the postulate of a “crack growth law” —a power-law relation between crack extension, Δa, and plastic displacement — used to express Jpl in terms of material properties, size parameters, and crack extension, giving rise to a Jpl-Δa analytical expression, similar to the power law J = C1(Δa)C2 suggested in ASTM Standard Test Method for Measurement of Fracture Toughness (E 1820). A few examples are included to show the use of the method, and comparisons are made with J-Δa curves calculated as per ASTM E 1820.