CONTENTS Introduction § 1. A short review of results § 2. Criteria for Fuchsian systems with regular singular points § 3. Preliminary information. The method of solution § 4. The solubility of the Riemann-Hilbert problem for an irreducible representation of dimension three § 5. Fuchsian systems of two equations on the Riemann sphere. The Fuchsian weight of a representation § 6. The Riemann-Hilbert problem for a system of three equations § 7. The Fuchsian weight and two-dimensional holomorphic vector bundles on the Riemann sphere Conclusion References