We report on our recent study on light bridges in emerging active regions. Light bridges, the bright structures dividing umbrae in sunspot regions, are known to produce wide variety of activity events. In order to reveal the nature of light bridges, we first analyze observational data of a light bridge in NOAA AR 11974 obtained by Hinode, SDO, and IRIS. We find that the bridge has a relatively weak horizontal field, which is transported to the solar surface by a large-scale convective upflow. This horizontal field is sandwiched between strong vertical fields of surrounding pores, showing a strong current layer. Above the bridge, we observe repeated chromospheric brightenings and dark surge ejections into the coronal heights. The detailed magnetic and velocity structures are then investigated by analyzing an MHD simulation data of a light bridge structure that appear in an emerging flux region. It is found that, during the formation of an active region, strong vertical fields trap a plasma upflow, which transports a weak horizontal field to the surface layer and creates a light bridge structure. The striking correspondence between observational and numerical results provides a consistent physical picture that the various activity events observed above the light bridge structures are caused by repeated magnetic reconnection that is driven by continuous magneto-convective evolution within the bridges.