Remember to do, remember doing, forget to do, forget doing: remember and forget are English verbs that can be followed both by a verb ending in -ing (a gerund) or by the infinitive form of the verb. 

However, there is a difference in meaning and that difference is connected with time.

Here is how to make sure you understand the difference and use them properly:

Remember / Forget doing:

Use remember and forget followed by a verb in -ing for something that has happened (past!). 

For example:

• I’ll never forget travelling across Europe. 
• I’ll always remember travelling across Europe.

→ Here, in both sentences, choose the gerund (-ing) travelling because it is something that you have done, that has happened (in the past)

Remember / Forget to do:

Use remember and forget followed by an infinitive for something that you need or needed to do, that has or had to be done.

For example:

• Don’t forget to call the agency. → you need to call the agency
• Oh I’m sorry, I forgot to post the letter! → I had to post the letter
• Remember to buy something to eat on your way back home. → You need to buy something to eat.

There you are! It’s as simple as that! You now know how to use the English verbs remember and forget. Congratulations! 😉