<prompt> Human: I assume the risk is greater the smaller amount onw buys, but whats the least someone can invest in buying debt, with the goal of getting a better ROI than a savings account, precious metals, or cryptocurrency dont hit me. Are tax lien certificates the way to start?  <response>: you can buy as little as 100 of US government debt You can buy some corporate bonds directly with low minimums. Solar City was selling solar bonds for 1k minimum - the risk is much higher than US bonds, you need to do your due diligence.Precious metals and cryptocurrencies dont have an expected ROI. They would more typically be used to hedge other risks.Honestly in my opinion your best bet to not get a bad deal is to find a bond mutual fund or bond ETF with your favored risk profile - US government, US inflation protected, municipal, high grade corporate, or junk corporateAnd there is a reason high yield bonds are called junk bonds. 