I. Periods of meromorphic functions.- § 1. Meromorphic functions.- § 2. Periodic meromorphic functions.- § 3. Jacobi's lemma.- § 4. Elliptic functions.- § 5. The modular group and modular functions.- Notes on Chapter I.- II. General properties of elliptic functions.- §1. The period parallelogram.- § 2. Elementary properties of elliptic functions.- Notes on Chapter II.- III. Weierstrass's elliptic function ?(z).- §1. The convergence of a double series.- § 2. The elliptic function ?(z).- § 3. The differential equation associated with ?(z).- § 4. The addition-theorem.- § 5. The generation of elliptic functions.- Appendix I. The cubic equation.- Appendix II. The biquadratic equation.- Notes on Chapter III.- IV. The zeta-function and the sigma-function of Weierstrass.- § 1. The function ?(z).- §2. The function ?(z).- § 3. An expression for elliptic functions.- Notes on Chapter IV.- V. The theta-functions.- §1. The function ?(?, ?).- § 2. The four sigma-functions.- § 3. The four theta-functions.- § 4. The differential equation.- § 5. Jacobi's formula for ?' (0, ?).- § 6. The infinite products for the theta-functions.- § 7. Theta-functions as solutions of functional equations.- § 8. The transformation formula connecting ?3(v, ?) and ?3(?, ?1/?) ..- Notes on Chapter V.- VI. The modular function J(?).- § 1. Definition of J(?).- § 2. The functions g2(?) and g3(?).- § 3. Expansion of the function J(?) and the connexion with theta-functions.- § 4. The function J(?) in a fundamental domain of the modular group ..- § 5. Relations between the periods and the invariants of ?(u).- § 6. Elliptic integrals of the first kind.- Notes on Chapter VI.- VII. The Jacobian elliptic functions and the modular function ?(?).- § 1.The functions sn u, en u, dn u of Jacobi.- § 2. Definition by theta-functions.- § 3. Connexion with the sigma-functions.- § 4. The differential equation.- § 5. Infinite products for the Jacobian elliptic functions.- § 6. Addition-theorems for sn u, cn u, dn u.- § 7. The modular function ?(?).- §8. Mapping properties of ?(?) and Picard's theorem.- Notes on Chapter VII.- VIII. Dedekind's ?-function and Euler's theorem on pentagonal numbers.- § 1. Connexion with the invariants of the ?-function and with the theta-functions.- § 2. Euler's theorem and Jacobi's proof.- § 3. The transformation formula connecting ?(z) and ?(?¿).- §4. Siegel's proof of Theorem 1.- §5. Connexion between ?(z) and the modular functions J(z), ?(z).- Notes on Chapter VIII.- IX. The law of quadratic reciprocity.- § 1. Reciprocity of generalized Gaussian sums.- § 2. Quadratic residues.- §3. The law of quadratic reciprocity.- Notes on Chapter IX.- X. The representation of a number as a sum of four squares ..- §1. The theorems of Lagrange and of Jacobi.- § 2. Proof of Jacobi's theorem by means of theta-functions.- §3. Siegel's proof of Jacobi's theorem.- Notes on Chapter X.- XI. The representation of a number by a quadratic form.- §1. Positive-definite quadratic forms.- § 2. Multiple theta-series and quadratic forms.- § 3. Theta-functions associated to positive-definite forms.- § 4. Representation of an even integer by a positive-definite form.- Notes on Chapter XI.- Chronological table.