To get the best quality espresso, not only do you need a great espresso machine but you also need to get quality coffee beans. Technically, you can put any regular coffee beans into your espresso machine. But you might not always be happy with the results as, depending on what you buy, your espresso coffee may be bitter or sour. There are, however, specific styles that will work best as espresso beans. Some coffee roasters will sell a specific espresso blend. But, if not, you want to go for a dark roast and preferably something that has been ethically sourced.  Regardless of what coffee beans you choose for your new espresso machine, you do need to buy finely ground coffee. Or, even better, grind it freshly yourself. If it's too coarse, you will under-extract and get a really weak coffee.