Can I hook up my stereo line-out to my Mac's line-in to record cassette tapes?

Can I hook up my stereo/boom-box's line-out (headphone) to my Mac's line-in (or microphone input)?

Update:

tl;dr: You can connect a "line-out" to a "line-in" and all will be well.

As slhck commented below, current MacBooks have a "line-in" socket that is for "a line-level microphone" which isn't your normal mic-in socket found on typical Windows/Linux PC hardware. A line-level input should be less vulnerable than a mic-level input (though it isn't designed for a headphone output expecting a 32-ohm impedance.) Designers of modern Macs and PCs probably make provision for end-users plugging inappropriate outputs into sensitive inputs

Normally, each of the following audio interfaces are different and (at least for quality reasons) should not be mixed up

• line-in and line-out
• headphone out
• microphone in

Each interface is electrically different.

Line-in is explicitly designed to be connected to line-out (on a different device usually) and vice versa. These are high-impedance, low-current signal interfaces.

Microphone-in is designed for connecting microphones, these produce much weaker signals than line-out and normally need pre-amplification before being fed to a line-in interface.

Headphone outputs are designed for relatively low-impedance devices that use a much higher signal level. It would normally be a bad idea to connect a headphone-output to a microphone-input, at best you should expect clipping and distortion.

I think some computers have connectors whose electronics can be switched in software to provide appropriate impedance etc for two different signal levels.

Update:

Stricly speaking, you should use impedance matching and attenuation in between headphone-out and microphone input. This can be done with attenuating leads, DI boxes etc

For example, the description of this product says

• Outputs Mic Level
• Speaker Level Input

Or this one

• Adjustable speaker simulation
• Balanced mic level output

Sure, just do it. You said you're on a Mac, which means that there's no separate input for microphone and line signals.

Just plug it in, using a stereo jack cable …

… and select the appropriate input source under System Preferences » Sound » Input. You should level the input volume so that there is no clipping (i.e. the bars shouldn't be full all the time).

And now you need a program to record. I suggest Audacity, which is free, open source, and comes for all operating systems.