The German Verb "Lassen"

There are a few alternative constructions to the passive voice in German. The verb “lassen” is one of these, which means “to let”; however, it is used differently here than in English. Consider the following examples:

Es lässt sich leicht erklären.
It lets itself be easily explained. (literal translation)

The English translation sounds awkward to any native English speaker — the better equivalent is: “It is easy to explain” or “it can easily be explained.” The passive voice uses past participles in both English and German, but the above formulation is constructed using a present tense reflexive verb and an infinitive (lässt/erklären; is/to explain). This German alternative to the passive voice is used in place of the modal verb “können” in the passive (e.g. Es kann nicht geschrieben werden. = Es lässt sich nicht schreiben.). Below are some more examples to give you an idea of how “lassen” is used:

Ich lasse mich beraten.
I am going to get advised/seek advice.

Lässt du dein Fahrrad reparieren?
Are you going to get/have your bicycle repaired?

Much like in the previous examples, the English equivalents are not word-for-word translations, but they convey approximately the same meaning: in both cases, the subject is not the one doing the activity (beraten, reparieren); but rather, they are having someone else perform those services, i.e. they are arranging for them to be done.

Used as a reflexive verb, “lassen” can refer to letting/allowing something to be done:

Sie lässt sich operieren. 
She is having surgery. (lit. She is letting herself get operated.)

Sie lassen sich scheiden.
They get/are getting divorced. (lit. They are letting themselves get divorced.)

Er lässt sich seine Haare schneiden.
He is getting a haircut. (lit. He is letting himself get his hair cut.)

Im Perfekt

To put the verb “lassen” in the past tense, conjugate the helping verb “haben” and place the infinitive “lassen” after the infinitive form of the main verb, creating a double infinitive. For example,

Sie lässt sich operieren. -> Sie hat sich operieren lassen.
She is having surgery. -> She got/had surgery. 

Ich lasse mein Auto in der Garage stehen. -> Ich habe mein Auto in der Garage stehen lassen.
I am leaving my car parked in the garage. -> I left my car parked in the garage.