If you are an employee in the United States, your employer is responsible for withholding taxes from your paycheck. However, there are a few reasons why taxes might not be withheld from your paycheck.
The first reason is that you may have claimed too many allowances on your W-4 form. When you claim allowances, your employer withholds less money from each paycheck for taxes. If you claim too many allowances, not enough money will be withheld for taxes and you may owe money at the end of the year.
Another reason taxes might not be withheld from your paycheck is if you owe back taxes to the IRS. If you owe back taxes, the IRS can instruct your employer to withhold a certain amount of money from each of your paychecks until the debt is paid off.
Lastly, if you have recently changed jobs, it's possible that your new employer hasn't received all of the necessary tax information from your previous employer yet. This can cause a delay in withholding taxes from your paycheck.
If none of these reasons apply to you and you're still not having taxes withheld from your paycheck, contact your employer or the IRS to find out what's going on.