To actively take part in something, participate, or get involved, often without having been explicitly asked to do so. The expression is usually used colloquially.
example
Bei der Diskussion über das neue Projekt wollte jeder mitmischen.
In the discussion about the new project, everyone wanted to join in.
Usage tips
Separable verb
'Mitmischen' (to join in / get involved) is a separable verb. The prefix 'mit-' comes at the end in a main clause. In subordinate clauses and in the infinitive with 'zu', the verb stays together.
EXAMPLE
Bei dieser Entscheidung mischt der Chef immer mit.
The boss always gets involved in this decision.
Word structure
The word is made up of the prefix 'mit-' and the verb 'mischen' (to mix). Here, the prefix 'mit-' means 'together with others' or 'being part of it', which makes the meaning 'to participate' logical.
EXAMPLE
In der Politik wollen viele neue Leute mitmischen.
In politics, many new people want to get involved.
Colloquial style
In the meaning of 'sich beteiligen' (to take part), 'mitmischen' (to join in / get involved) is clearly colloquial. It sounds active and sometimes also a little cheeky or self-confident.
EXAMPLE
Unser kleines Team mischt jetzt bei den Großen mit.
Our small team is now joining in with the big players.
Use with 'bei'
If you want to say what someone is taking part in, you usually use the preposition 'bei' followed by the dative.
EXAMPLE
Er will bei der Planung des Festes unbedingt mitmischen.
He absolutely wants to get involved in planning the party.
Compare with
near_synonym
mitmischen vs teilnehmen
to participate / sympathize
'teilnehmen' and 'mitmischen' can both mean that someone is part of something and does something. 'teilnehmen' sounds neutral and fits well with courses, events, competitions, or official activities. 'mitmischen' is more colloquial and emphasizes that someone actively has a say or gets involved, sometimes even without a clear invitation. If you only want to say that someone is present at a course or appointment, 'teilnehmen' is more natural. If someone gets heavily involved or actively tries to influence things, 'mitmischen' fits better.
mitmischen
Bei der Planung des Straßenfests will auch der neue Nachbar mitmischen.
The new neighbor also wants to get involved in planning the street festival.
teilnehmen
Trotz des schlechten Wetters nehmen viele Kinder am Training teil.
Despite the bad weather, many children are taking part in the training.