vollziehen
to carry out
To carry out or implement an official action, decision, or formal act. This word is mainly used in formal or official contexts.
Der Standesbeamte vollzog die Trauung.
The registrar conducted the wedding ceremony.

to carry out / take place
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to carry out
To carry out or implement an official action, decision, or formal act. This word is mainly used in formal or official contexts.
Der Standesbeamte vollzog die Trauung.
The registrar conducted the wedding ceremony.

'Vollziehen' is an inseparable verb. The prefix 'voll-' stays firmly attached to the verb in all tenses and sentence types and is never placed at the end of the sentence.
Der Richter vollzieht das Urteil.
The judge enforces the judgment.
This verb belongs to formal language (elevated language, official language). In normal everyday speech, you would use simpler verbs like 'machen' (to do/make), 'ausführen' (to carry out), or 'durchführen' (to carry out/conduct).
Der Priester vollzog die heilige Zeremonie.
The priest conducted the holy ceremony.
In the meaning 'geschehen' (to happen), the verb is always used reflexively with 'sich'. The subject of the sentence is then the process or change itself.
Ein tiefgreifender Wandel vollzieht sich in der Arbeitswelt.
A profound change is taking place in the world of work.
You can recognize the meaning from the sentence structure: the reflexive form 'sich vollziehen' always means 'geschehen' (to happen). If the verb appears with an accusative object such as 'Trauung' (wedding ceremony) or 'Urteil' (judgment), it means 'ausführen' (to carry out).
Ein Generationswechsel vollzieht sich in der Firma.
A generational change is taking place in the company.
In formal contexts, 'vollziehen' is often combined with certain nouns. Typical phrases are 'eine Handlung vollziehen' (to perform an action), 'einen Akt vollziehen' (to carry out an act), or 'eine Wende vollziehen' (to make a shift/turnaround).
Mit dieser Entscheidung vollzog die Regierung eine politische Wende.
With this decision, the government made a political shift.
to happen
'geschehen' and 'sich vollziehen' can both express that something takes place. 'geschehen' is more general and can be used for many individual events. 'sich vollziehen' sounds more formal and usually describes a process or change that is not suddenly complete. It is especially appropriate when something develops slowly or step by step. In everyday language, people often say 'geschehen'; in texts about society, politics, or personal changes, 'sich vollziehen' sounds more precise.

Der Wandel in der Firma vollzieht sich seit mehreren Jahren.
The change in the company has been taking place for several years.
Während der Sitzung ist nichts Besonderes geschehen.
Nothing special happened during the meeting.