In the Standard Model, there is only one SU(2) scalar doublet involved in the EWSB and will only predict one physical scalar particle, the Higgs boson. The LHC had probed the Higgs and it fits well with the data. Even though we only probe one scalar boson now, there can be more scalars, light scalars, exotic Higgs and charged Higgs. In this talk, I will introduce scalar-scalar interactions, its current constraints and phenomena at the LHC.