The most important aspect of disulfide bonds is their scission, as the  bond is usually the weakest bond in a molecule.  Many specialized organic reactions have been developed to cleave the bond.  
A variety of reductants reduce disulfides to thiols.  Hydride agents are typical reagents, and a common laboratory demonstration "uncooks" eggs with sodium borohydride.  Alkali metals effect the same reaction more aggressively:  followed by protonation of the resulting metal thiolate:   
In biochemistry labwork, thiols such as β-mercaptoethanol (β-ME) or dithiothreitol (DTT) serve as reductants through thiol-disulfide exchange.  The thiol reagents are used in excess to drive the equilibrium to the right: 
The reductant tris(2-carboxyethyl)phosphine (TCEP) is useful, beside being odorless compared to β-ME and DTT, because it is selective, working at both alkaline and acidic conditions (unlike DTT), is more hydrophilic and more resistant to oxidation in air. Furthermore, it is often not needed to remove TCEP before modification of protein thiols.
In Zincke cleavage, halogens oxidize disulfides to a sulfenyl halide:
More unusually, oxidation of disulfides gives first thiosulfinates and then thiosulfonates:
:RSSR + [O] → RS(=O)SR
:RS(=O)SR + [O] → RS(=O)SR