Create unobstructed views of multiple components of one plot or lighten a single plot component against the background.

Using 2D Plots...

Create a plot

Use Plot to create a graph of x^2:

Add options to the plot

Use the PlotStyle option with Opacity to make the plot 70% transparent:

Add different transparency settings for plots of multiple functions:

Using 3D Plots...

Create a plot

Use Plot3D to create a graph of the polynomial x^4-5x^2y^2+y^4:

Add options to the plot

Use the PlotStyle option with Opacity to make the plot 70% transparent:

Add different transparency settings for plots of multiple functions:

Using Graphics...

Create a disk graphic

Apply Graphics to Disk to render a unit disk:

Add options to the graphic

Make a 75% transparent disk:

Opacity can have values between 0 and 1, with 0 corresponding to perfect transparency:

Use Opacity with a color:

Notes

Opacity interacts well with other functions: