When introducing a sentence with an adverbial participle phrase, add a comma after it. In the middle or at the end of a sentence, commas are frequently unnecessary.

When introducing a sentence with an adverbial participle phrase, add a comma after it.

Having spent two years abroad, Rebecca was ready to come home again.

Having spent two years abroad Rebecca was ready to come home again.

In the middle or at the end of a sentence, commas are frequently unnecessary.

I ran into an old friend while visiting Chicago's Art Institute.

1. Participial Phrases as Adverbs

Participles themselves (e.g., “walking” or “walked”) can function as adjectives, but not adverbs.

Olivia is confused.

However, participle phrases can function as adverbs.

Using critical thinking, he identified the best solutions.

In the example above, “using critical thinking” is an adverbial phrase containing a participial form.

2. Commas at the Beginning of a Sentence

When starting a sentence with an adverbial participle phrase, place a comma after it.

Hearing about the new company policies, the employees complained about increasingly difficult working conditions.

It is possible to drop the comma if the introductory phrase is short (no more than three or four words) and clear.

Exiting a parking lot she had an accident.

But use a comma to avoid confusion or signal that the adverbial participle phrase describes the whole sentence that follows.

Driven by ambition, John is constantly striving to reach his goals through hard work.

3. Participial Phrases in the Middle or at the End of a Sentence

We do not generally need commas when using a participial phrase in the middle or at the end of a sentence.

I ran into my ex-husband while shopping at the mall.

But use commas to set off an adverbial participle phrase to:

• add nonessential information
• interrupt the sentence flow
• avoid confusion
• signal that the phrase modifies the entire sentence and not just a word

We lingered for a while at the table, after finishing our meal, to discuss current and emerging issues.

We relaxed for the first time in years, walking through the countryside, and enjoyed a wonderful conversation.