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If you speak some German, you will inevitably encounter the question whether you ought to address people as "Du" (informal) or "Sie" (formal). The key is your closeness with your contact. If it is an older person, it is always polite to address them as "Sie" - unless your contact offers the more informal "Du" to you first. The rule is that only 'superior' people (e.g. those with more status, or older than you) can offer this. "Du" is very common among students in their twenties. There is also a tendency to use "Du" all over the workplace, but that does not change the existing hierarchy at all, thus it should be avoided. What is to be avoided at all cost is to get friendly with your co-workers/bosses at an "office party", switch to the "Du' and carry it over to the normal office routines. Believe me, it just does not work.