Kamala Harris will make history when she takes the oath of office on Wednesday, becoming the first woman and first black and South Asian American to serve as US vice-president. Here's what awaits Ms Harris in her new job. What does a vice-president do? Historically speaking, not a lot. It has been described as the least understood, most ridiculed and most often ignored constitutional role in the federal government, and for a long time it stayed that way. "The role of the vice-president was, frankly, to just be that heartbeat away from the president," said Barbara Perry, the director of presidential studies at the University of Virginia's Miller Centre. Unless the president died, or was seriously ill, the vice-president's job was largely to sit around and wait. For some vice-presidents, the dynamic meant holding a job you hoped would never be needed. "One of the vice-presidents in the early 20th Century said, 'Every day I ring the doorbell at the White House and hope the president will answer,'" Ms Perry said. That's not a role to take lightly. Nine of the country's 45 presidents has left office before the end of their term, eight by death - about one fifth of all presidents - giving their vice-presidents a sudden promotion. At 78 years old, Mr Biden will be the oldest president to assume the office, putting added stress on his next-in-line. It wasn't until the 1970s, under President Jimmy Carter, that the vice-president began to assume a bigger role. Mr Carter, a former Georgia governor, had built his candidacy around being a political outsider. "He knew he didn't know Washington," Ms Perry said. So when he won the nomination, he called on Walter Mondale, a long-time US senator, to show him the ropes and be a "true governing partner". While their close relationship was new, their strategic match followed a well-worn pattern of vice-presidents offering geographical or ideological balance to the president. The practice has continued on most recent political tickets. Barack Obama, then a relative political newcomer, tapped Joe Biden, a 35-year veteran of the US Senate. Donald Trump went with Mike Pence, whose evangelical bona fides were thought to smooth over Mr Trump's image for the religious right. And Ms Harris offers a counter to Joe Biden's age, gender and race. What's more, this time the ceremonial role held by the vice-president as president of the Senate will prove crucial for Ms Harris' party. There is currently a 50-50 seat split between Democrats and Republicans in the upper chamber, and Ms Harris will cast the deciding ballot in any tie. Where do they live? Ms Harris and her husband Doug Emhoff will set up home in a different white house - a 19th Century mansion on the grounds of the US Naval Observatory in north-west Washington. The estate is close to the White House grounds, where Ms Harris will have her office, and not far from Georgetown University's law school, where Mr Emhoff, an attorney, is set to teach. To get around, Ms Harris and Mr Emhoff will also have access to Air Force Two, a Boeing 757, and they will have round-the-clock security.