Justin Mamis independently publishes The Mamis Letter weekly, as well as other opinion products. Quotes from The Mamis Letter have appeared frequently in Barron's and the Wall Street Journal, and his often heretical and usually grumpy comments have been heard from time to time on CNBC.

After serving as Assistant Director of the NYSE Floor Department, Justin Mamis founded the Professional Tape Reader in 1972, selling it in 1977 when he thought he was going to retire. Getting bored, he returned to New York as an "upstairs" Member-Trader for Phelan, Silver - a NYSE specialist firm - and subsequently spent several not particularly skillful months as an options trader on the AMEX floor, before gradually settling into his role as market advisory letter writer, forecaster, and philosopher on behalf of, in succession: Wertheim & Co., Cowen & Co., Gordon Capital, and Hancock Institutional Equity Services. In that time period, he was regularly elected to the Institutional Investor "All-Star Team” in the categories of Market Timing and Market Technician. Since 1996, Justin has provided his opinions to institutional investors via his independently-owned company, Noah Financial, LLC.

Justin has been a prolific writer in the business and investing arena. The original edition of When to Sell was first published in 1977 (Farrar, Straus & Giroux); it was updated (Third Edition) in 1999 and published by Fraser Publishing (www.fraserpublishing.com). When to Buy was published by Farrar, Straus & Giroux in 1982; a Second Edition was published in 2001 by Fraser. His personal favorite – because it is more philosophical in tone – is The Nature of Risk - Stock Market Survival &. The Meaning of Life (published in 1991 by Addison Wesley, and updated from the original publication by Fraser Publishing in 1999). A self-published (in 1995) collection of "Ten Sermons by a Non-Rabbi" includes a "Stock Market Sermon."