It is well known that symmetry provides useful guidance to organize quantum phases of matter and leads to many important physical implications such as conservation laws and constraining low-energy dynamics of a quantum field theory. Recently, remarkable progress has been made in generalizing the concept of symmetry and elucidating its connection to topological defects. In this talk, I will discuss a recent progress on a holographic principle for generalized global symmetry, dubbed as topological holography, which describes the generalized symmetry of a quantum system in terms of a topological order in one higher dimension. This framework separates the topological data from the local dynamics of a theory and provides a unified description of the symmetry and duality in gapped and gapless phases of matter. In particular, I will focus on various exotic quantum critical points and gapless phases in (1+1)d such as phase transitions between symmetry protected topological (SPT) phases, symmetry enriched quantum critical points, deconfined quantum critical points and intrinsically gapless SPT phases. I will also discuss a topological holographic picture for conformal boundary states of (1+1)d rational conformal field theories, and uncovers the correspondence between the nature of the (1+1)d gapped phases and the boundary states.