Wunderlist is now on the real verge of being shutdown by Microsoft and Todoist claims to be import compatible. One thing to know is that Todoist Free has a limit of 50 lists. If you've used Wunderlist for any number of years then you may find your import failing. Two options:

  1. Merge lists in Wunderlist before importing (I think the limit is the number of discrete lists not the total number of list items)
  2. Buy Todoist paid edition (I did only the first paid edition) before you import

If you import and you get a Failed Import message then that's the sign that you need to do either 1 or 2. The first time I imported, import failed without any feedback. Props to Todoist for fixing this pretty quickly and that's the reason I paid.