Learn Hardcore German: Mein Chef ist heute im Büro.

German possessive pronouns agree in gender, number, and case with the noun they modify. Chef is a masculine noun in the nominative case, so you use mein (no –e ending). If it were a feminine noun (e.g. Chefin), you would say meine.

Why is Chef capitalized?

In German, all nouns—no matter where they appear in a sentence—are always capitalized. That’s why Chef (meaning “boss”) has a capital C.

What is im and why didn’t the sentence just say in dem?

im is the contraction of in + dem.

in (in) + dem (the‑dative singular)
Use this when indicating a static location (answering “Wo?”).

Which case is Büro in and how can I tell?

Büro is in the dative case. Clues:

The preposition in with a location (Wo?) triggers dative.
You see it in the article: dem Büro, contracted to im Büro.

Why is the verb ist in the second position?

German main clauses follow the V2 rule: the finite verb must be the second element. Here the first element is the subject (Mein Chef), so ist comes next.

Why does heute come between ist and im Büro?

German adverbs have a typical order:

Temporal (time)
Modal (manner)
Lokal (place)

Since heute is a time adverb, it naturally follows the verb and precedes the place phrase im Büro.

Why didn’t we say Mein Chef arbeitet heute im Büro?

Both sentences are correct but mean slightly different things:

Mein Chef ist heute im Büro. → He is in the office today (location).
Mein Chef arbeitet heute im Büro. → He is working in the office today (activity).

Can I start the sentence with Heute instead?

Yes. If you front Heute, you still keep the verb in second position:
Heute ist mein Chef im Büro.

How would I refer to a female boss?

Use the feminine form Chefin and the possessive meine:
Meine Chefin ist heute im Büro.

How do I turn this into a yes/no question?

In German you invert subject and verb, putting the verb first:
Ist mein Chef heute im Büro?