StreamPlot

StreamPlot[{v_x,v_y},{x,x_min,x_max},{y,y_min,y_max}]

generates a stream plot of the vector field {v_x,v_y} as a function of x and y.

StreamPlot[{{v_x,v_y},{w_x,w_y},…},{x,x_min,x_max},{y,y_min,y_max}]

generates plots of several vector fields.

StreamPlot[…,{x,y}∈reg]

takes the variables {x,y} to be in the geometric region reg.

Details and Options

StreamPlot plots streamlines that show the local direction of the vector field at each point.
StreamPlot by default shows enough streamlines to achieve a roughly uniform density throughout the plot, and shows no background scalar field.
StreamPlot does not show streamlines at any positions for which the v_i etc. do not evaluate to real numbers.
StreamPlot treats the variables x and y as local, effectively using Block.
StreamPlot has attribute HoldAll, and evaluates the v_i etc. only after assigning specific numerical values to x and y.
In some cases it may be more efficient to use Evaluate to evaluate the v_i etc. symbolically before specific numerical values are assigned to x and y.
StreamPlot has the same options as Graphics, with the following additions and changes:

AspectRatio	1	ratio of height to width
EvaluationMonitor	None	expression to evaluate at every function evaluation
Frame	True	whether to draw a frame around the plot
FrameTicks	Automatic	frame tick marks
Method	Automatic	methods to use for the plot
PerformanceGoal	$PerformanceGoal	aspects of performance to try to optimize
PlotLegends	None	legends to include
PlotRange	{Full,Full}	range of x, y values to include
PlotRangePadding	Automatic	how much to pad the range of values
PlotTheme	$PlotTheme	overall theme for the plot
RegionFunction	True&	determine what region to include
StreamColorFunction	None	how to color streamlines
StreamColorFunctionScaling	True	whether to scale the argument to StreamColorFunction
StreamMarkers	Automatic	shape to use for streams
StreamPoints	Automatic	determine number, placement, and closeness of streamlines
StreamScale	Automatic	determine sizes and segmenting of individual streamlines
StreamStyle	Automatic	how to draw streamlines
WorkingPrecision	MachinePrecision	precision to use in internal computations