Find the logarithm. \[ \log _{10} 0.001 \]

Step 1 ：Find the logarithm base 10 of 0.001. This is asking the question: 10 to what power equals 0.001?

Step 2 ：We know that 10 to the power of -3 equals 0.001.

Step 3 ：Therefore, the logarithm base 10 of 0.001 should be -3.

Step 4 ：Final Answer: \(\boxed{-3}\)