The penetration of small-scale Distributed Generation (DG) such as photovoltaics (PVs) has increased dramatically in recent years and is expected to increase further in the future. Small numbers of DG cause few or no problems to the grid, but as the percentage of DG grows, power quality, protection, and safety concerns need to be evaluated. A number of software tools are available to perform a distribution system analysis with varying degrees of complexities -ranging from relatively simple screening analysis to sophisticated transient simulations. This presentation will review the type of planning tools that are available and inform which ones are suitable for the investigation of a particular DG impact. Furthermore, the presentation will discuss how Distribution System State Estimation in combination with sensor data collected on distribution circuits can be used in an operational environment to (1) improve distribution system models and (2) inform control decisions of Grid Management Systems.