Html.Partial returns a String. Html.RenderPartial calls Write internally and returns void.

The basic usage is:

// Razor syntax
@Html.Partial("ViewName")
@{ Html.RenderPartial("ViewName");  }

// WebView syntax
<%: Html.Partial("ViewName") %>
<% Html.RenderPartial("ViewName"); %>

In the snippet above, both calls will yield the same result.

While one can store the output of Html.Partial in a variable or return it from a method, one cannot do this with Html.RenderPartial.

The result will be written to the Response stream during execution/evaluation.

This also applies to Html.Action and Html.RenderAction.