The wake behind a moving obstacle is a classic problem in fluid dynamics. Various flow regimes are classified by the dimensionless Reynolds number Re = vD/ν, where v is the obstacle velocity, D is the lateral dimension of the obstacle, and ν is the fluid viscosity. At low Re < 50, a laminar or steady flow is formed, and as Re is increased, periodic shedding of vortices with alternating circulation occurs, which is known as a von Karman vortex street. With further increasing Re > 105, the wake dynamics becomes unstable and turbulent flow develops. The transition from laminar to turbulent flow represents a universal characteristic of classical fluid dynamics. An interesting situation arises when a fluid has zero viscosity; i.e., it becomes a superfluid, where the Reynolds number cannot be defined and furthermore, vorticity is restricted with quantized circulation. In this talk, I will present a series of vortex-shedding and turbulence experiments which we have carried out with atomic Bose-Einstein condensates, where we observed a regular-to-turbulent transition of vortex shedding pattern and spatial pair correlations of vortices and antivortices in 2D superfluid turbulence.