Most income is taxable, whether you earn it or are paid as a return on your investment. Also, you generally have to pay tax on income when you sell something for more than your basis (usually the amount you paid for something).
If a type of income is taxable, it doesn't matter if you receive payment in cash, by check or electronic payment, or in the form of goods or services. You still pay tax on it.
Certain types of income are excluded from tax. This generally includes income you or someone else has already paid tax on, or income from special situations, such as combat pay.
Check this list to see if you have to pay tax on various types of income you may receive:
Dividends are not taxable when they are a return of capital. In other words, you don't pay tax when you are receiving back part of your investment, because it is not a share of profits.