If you need to print in black and white in OS X, you can, but it may not be obvious how to do it.
Apple used to include an obvious setting in its print dialog boxes for color or black and white, but in OS X this has disappeared since these options are now handled by the specific driver for your printer.
You can certainly still print in grayscale and there are various ways to do it, although some of these options might be a bit obscure, may only be available on some systems, or might require a few extra steps.
Some printer drivers support grayscale options, but these depend on the device being used and may not be obvious or may not be available. For instance, my Brother MFC color printer has a Print Settings option to change the color to "Mono" so only black toner is used; however, my Xerox Phaser's options are a bit more obscurely hidden in its Image Quality option, where the black-and-white option is available as a "Color Correction" setting. For more generic printer drivers there may be no options like this.
Because these device-specific options are present in a number of printer drivers (especially on color printers), first check the device-specific settings to see if one exists for your system. When you invoke the print dialog window by pressing Command-P in a document, click the Show Details button and then click the menu under the page orientation settings. The options in this menu should be categorized by those for the application, then the generic print options, followed by device-specific options, and finally the device status options. Most of the time the option for black-and-white printing will be in one of the device-specific options.
Unfortunately some printer drivers may not have these options, in which case alternative approaches to printing grayscale or black and white can be done by modifying and removing colors from the document itself.
Removing colors from images
If the document you are printing is just a rasterized image such as a JPEG file, then you can easily force it to be black and white by adjusting the color settings on the image. Open the image in Preview, go to the Tools menu, and choose the "Adjust Color..." option. Then locate the Saturation setting and drag the slider completely to the left, which will pull all colors out of the image and leave it as a black-and-white document. From here you can print it in grayscale; however, do keep in mind that while the image will be monochromatic, if you haven't chosen a specific option for black and white then your printer will still use color inks to print it.
Using Quartz filters
The color saturation options are only available for rasterized image formats and will not be available for other formats like PDF that use vector graphics, embedded fonts, and other dynamically sizable contents. However, for these documents you can take advantage of Apple's Quartz filters to create a black-and-white PDF from any document, which can then be distributed electronically or printed.
To use Quartz filters, in any document invoke the print dialog box and then use the PDF menu at the bottom of the window to open it as a PDF in Preview. When the PDF is opened, choose Export from the File menu and make sure the format for the exported document is PDF. Then locate the Quartz Filter menu and choose either Black & White or Gray Tone. The Black & White filter will not have any gradients in it and the resulting document will look like an old photocopy of your original, but the Gray Tone option will contain the smooth gradients.
As with printing adjusted rasterized images, keep in mind that unless your printer device supports a true monochromatic option like Black & White or Grayscale, then even though the edited PDF document will print without colors, the printer may still use color inks to render the final product.