Monolayer molybdenum disulphide (MoS₂) exhibits valley-selective circular dichroism (CD), a key property for valleytronics, which is a new field of electronics that exploits the valley degree of freedom of charge carriers. This study demonstrates that MoS₂ is an ideal material for valleytronics due to its unique symmetry and the ability to achieve valley polarization through valley-selective CD. Experimental evidence is provided by measuring circularly polarized photoluminescence, which shows up to 50% polarization. The key to valleytronics is the non-equilibrium charge carrier imbalance between valleys. The principal mechanism involves circularly polarized optical excitation, where the two valleys absorb left- and right-handed photons differently, a phenomenon known as circular dichroism. An essential condition for valley-selective CD in a honeycomb lattice is the absence of a centre of inversion. In the case of graphene, this can be achieved by interacting with a substrate, but this is challenging experimentally. Monolayer MoS₂ has an indirect bandgap in the bulk but acquires a direct bandgap when thinned to the monolayer limit. This makes it a promising material for exploring novel electronic and optoelectronic devices. The natural stable structure of free-standing monolayer MoS₂ is a honeycomb lattice with inequivalent bipartite colouring, breaking the inversion symmetry. The study uses first principles calculations and experimental micro-photoluminescence to show that monolayer MoS₂ possesses near-perfect valley-selective CD. This is rooted in its bulk symmetry and is conducive to optoelectronic valley polarization. The degree of circular polarization is defined as the difference between the absorption of left- and right-handed light, normalized by total absorption. The optical selection rule is rooted in the phase winding of the Bloch states under rotational symmetry. The chiral optical selectivity of the valleys is deduced from the symmetry of the material. The bottom of the conduction bands at the valleys, dominated by the l=0 d-states on Mo, bears an overall azimuthal quantum number m±=±1, while the top of the valence bands has m±=0. This leads to angular momentum selection rules that indicate the absorption of left- and right-handed photons. The experimental measurements of circularly polarized photoluminescence confirm the theoretical predictions, showing a substantial circular polarization (η~50%) at the PL peak. The study also discusses the Berry curvature, which has crucial influence on the electronic transport properties. The presence of non-vanishing Berry curvature is possible in the non-centrosymmetric honeycomb lattice. The study concludes that MoS₂ is a promising material for valleytronics, and further experiments are suggested to explore the valley lifetime and other properties. The results highlight the potential of MoS₂ and other transition metal dichalcogenides for exploring valley physics.Monolayer molybdenum disulphide (MoS₂) exhibits valley-selective circular dichroism (CD), a key property for valleytronics, which is a new field of electronics that exploits the valley degree of freedom of charge carriers. This study demonstrates that MoS₂ is an ideal material for valleytronics due to its unique symmetry and the ability to achieve valley polarization through valley-selective CD. Experimental evidence is provided by measuring circularly polarized photoluminescence, which shows up to 50% polarization. The key to valleytronics is the non-equilibrium charge carrier imbalance between valleys. The principal mechanism involves circularly polarized optical excitation, where the two valleys absorb left- and right-handed photons differently, a phenomenon known as circular dichroism. An essential condition for valley-selective CD in a honeycomb lattice is the absence of a centre of inversion. In the case of graphene, this can be achieved by interacting with a substrate, but this is challenging experimentally. Monolayer MoS₂ has an indirect bandgap in the bulk but acquires a direct bandgap when thinned to the monolayer limit. This makes it a promising material for exploring novel electronic and optoelectronic devices. The natural stable structure of free-standing monolayer MoS₂ is a honeycomb lattice with inequivalent bipartite colouring, breaking the inversion symmetry. The study uses first principles calculations and experimental micro-photoluminescence to show that monolayer MoS₂ possesses near-perfect valley-selective CD. This is rooted in its bulk symmetry and is conducive to optoelectronic valley polarization. The degree of circular polarization is defined as the difference between the absorption of left- and right-handed light, normalized by total absorption. The optical selection rule is rooted in the phase winding of the Bloch states under rotational symmetry. The chiral optical selectivity of the valleys is deduced from the symmetry of the material. The bottom of the conduction bands at the valleys, dominated by the l=0 d-states on Mo, bears an overall azimuthal quantum number m±=±1, while the top of the valence bands has m±=0. This leads to angular momentum selection rules that indicate the absorption of left- and right-handed photons. The experimental measurements of circularly polarized photoluminescence confirm the theoretical predictions, showing a substantial circular polarization (η~50%) at the PL peak. The study also discusses the Berry curvature, which has crucial influence on the electronic transport properties. The presence of non-vanishing Berry curvature is possible in the non-centrosymmetric honeycomb lattice. The study concludes that MoS₂ is a promising material for valleytronics, and further experiments are suggested to explore the valley lifetime and other properties. The results highlight the potential of MoS₂ and other transition metal dichalcogenides for exploring valley physics.