As the national tax deadline looms, ProPublica has released new entries in its yearlong library of stories and easy-to-read graphics based on Internal Revenue Service files from 2013 to 2018. The stories from the nonprofit news sites’ reporters and data analysts explains who are the billionaires, how they got that way and how they are taxed. It’s instructional on how and why the policies over time became the tax code we all rely on.

If you’re reading about President Joe Biden’s push to enact a flat tax for billionaires as well as the other plans suggested this campaign year, this package will help you figure out what you believe about the code and how it can evolve for all. Keep in mind, billionaires are in is a pretty lofty space: It will take the average American 25,000 years to earn a $1 billion.

Here’s a list and links to the stories so you can work through them as you choose.

America’s highest earners and their taxes revealed: A look at who the earners are, how their wealth is taxed and why the rates differ. A basic primer on the system as it affects those with more than average earnings from wages and investments.

America’s top 15 earners and what they reveal about the U.S. tax system: Leaked IRS data shows tho reported the most income in America from 2013-2018, as well as their tax rates.

The great inheritors: How three families shielded their fortunes from taxes for generations: A history lesson on the tax avoidance and savvy investing that highlights the conflict between keeping the fortune you earned and contributing fairly to the public good.

How these ultrawealthy politicians avoided paying taxes: Through the holdings of two governors and a former cabinet member, this story guides us through how politicians exploit loopholes in the code and have access to knowledge that helps them build wealth on the taxpayers’ time.

These real estate and oil tycoons avoided paying taxes for years: This story spotlights the world of the ultrawealthy where generating millions can show up as major losses on a tax filings.

The billonaire playbook: How sports owners use their teams to avoid millions in taxes: Owning a sports franchise may seem like a vanity purchase to most of us, but it’s real business and there are lucrative tax reasons the sports world draws so many wealthy investors.

The secret IRS files: Trove of never-before-seen records reveal how the wealthiest avoid income tax: This is the first of the stories from the load of IRS files leaked to ProPublica. it revealed that billionaires Elon Musk, Jeff Bezos, Michael Bloombert, Carl Icahn and George Soros have managed to avoid federal tax completely at various times over the years. The story takes us through how that happens and “demolishes the cornerstone myth of the American tax system: that everyone pays their fair share and the richest Americans pay the most.”

The Tide brings regular notes and observations on news and events by The Current staff.