Make a 50% transparent sphere:

Plot a see-through surface:

Overlapping translucent 2D disks:

Larger opacity makes surfaces more opaque:

Opacity is kept throughout the scope of graphics directives:

Color primitives can be used with Opacity:

Directive can be used to combine colors with opacity:

Half-transparent surface:

Use Opacity to understand complicated surfaces:

Use Opacity to visualize internal structure, in this case two ellipsoidal shells:

Overlapping of translucent red and blue disks results in purple:

Background color can be seen through a transparent object:

Opacity plus color can also be specified using the optional final parameter of various color directives:

Each color primitive supports an extended form that can be used to specify opacity:

Opacity is used by default to show overlapping fillings:

Opacity is used for fillings to surface plots:

Opacity is used in ParametricPlot to visualize regions that get covered multiple times:

If the opacity is too small, objects will typically render as completely transparent:

Overlapping of multiple translucent objects can generate an opaque result:

If each opacity is too small, any number of elements together will still render as transparent:

Completely transparent objects are still counted for PlotRange:

The two-argument form of Opacity might be partially modified by subsequent directives:

The default rendering of opacity may clip objects that are behind too many other objects in 3D graphics:

Rendering can be improved by increasing the depth peeling layers with RenderingOptions:

Alternatively, the graphic can be rendered using a BSP tree, which is slower but has no layer limit:

Random collection of transparent cylinders: