I currently have a maxed employee-matched 401K, and a maxed IRA, plus an emergency fund. Is the next step to invest in the stock market?

Congratulations on maxing out your 401k/IRA! You seem to be well on track financially.

The next step depends on what your financial goals are. Here are a few options you can consider:

- To achieve tax diversification during retirement, you may want to consider setting up a Roth IRA. As you have maxed out your IRA limit for the year, you can do a Roth conversion, or start to contribute to your Roth next year. This will allow you the flexibility to choose to withdraw from a pre-tax or post-tax account during retirement. 

- Do you have any other pressing financial needs? Do you have any non-mortgage debt? Are you saving for college, planning on buying a new home in the near future? If so, you may want to set some extra cash aside for such purposes and avoid taking on high-interest debt.

- Taxable stock investments can also be a good way to grow your money. When you invest outside of a retirement fund, you can choose to withdraw the money out at any point, without any penalty. However, keep in mind that taxes will apply, so you need to consider different tax planning strategies to make it worthwhile.

- Consider other investments: When investing outside of retirement funds, you can choose almost any types of investments. Many investors choose to go with real estate, private placements and other options, beyond stocks and bonds. Keep in mind that whichever investments you choose, be sure to perform due diligence to minimize the risk to your savings. 

From experience, i'm going to believe that your 401(k) and IRA are all in vested in either stocks and/or bonds. For that reason, my suggestion is your next investments should be in assets other than those you are currently in.

What you should be seeking is "non-correlation" or assets whose prices are not dependent on earnings like stocks or interest rates such as bonds. That used to be difficult to do prior to the advent of Exchange Traded Funds (ETF's). One of the most succcessful college endowments for years has had less than half of their portfolio in stocks and bonds. They have invested in things like timber, venture capital or so-called alternative investments. Those types of investments were out of reach of retail investors prior to the advent of ETF's. But you can invest in timber through the WOOD ETF, venture capital, real estate, futures and numerous other assets to further diversify a portfolio.

If  this interests you, check the website www.etf.com and do some research on alternative ETF investments.