We study the holomorphic sections of the Deligne-Hitchin moduli space of a compact Riemann surface, especially the sections that are invariant under the natural antiholomorphic involutions of the moduli space. Their relationships with the harmonic maps are established. As a by product, a question of Simpson on such sections, posed in [Si4], is answered.The other complex structure J on M SD arises from the identification of M SD with the moduli space of flat complex connections due to a result of Donaldson, [Do], in the case of rank n = 2 and by a result of Corlette in general [Co]. The third complex structure K is of course K = IJ = −JI. The significance of the self-duality equations in mathematics and theoretical physics is primarily due to, to quote Hitchin, the various incarnations of the solutions, bringing together geometry, topology, analysis and algebra in a harmonious way.Every hyper-Kähler manifold M has a twistor space associated to it. Topologically it is just the product of the space M with the 2-sphere:It has a tautological complex structure given by the natural complex structure on the 2sphere and the above complex structure xI p + yJ p + zK p on M × {(x, y, z)}; the natural projection of the twistor space to CP 1 is evidently holomorphic. The importance of the twistor space construction is due to the fact that the hyper-Kähler structure is encoded in holomorphic data on the twistor space. In the case of the moduli space of solutions to the self-duality equations, the corresponding twistor space, which is known as the Deligne-Hitchin moduli space and is denoted by M DH , admits another interpretation which is due to Deligne; see [Si2]. From Deligne's perspective, this Deligne-Hitchin moduli space M DH is considered as the moduli space of λ-connections on the Riemann surface Σ glued with the moduli space of λ-connections on the conjugate Riemann surface Σ via the Riemann-Hilbert isomorphism; for definitions and details see Section 1. As a consequence, integrable surfaces like harmonic maps and minimal surfaces can be described by sections of the twistor space M DH −→ CP 1 satisfying certain reality conditions that depend on what the target space is. We note that for the case of G C = SL(2, C), these surfaces are lying in any of the following: S 3 , H 3 and its quotients, and their Lorentzian counterparts.