The World Trade Center was indeed the tallest building in the world until it's demise in 2001 due to the attacks.
The World Trade Center stood at a height of 1,368 feet for the 1 World Trade Center and for the 2 World Trade Center it stood at a height of 1,362 feet tall.
So both World Trade Center buildings were pretty tall buildings and were considered to be the tallest buildings in the world.
That is until in the year 2004 when the construction started on the now tallest building in the world which is the Burj Khalifa building that stands a staggering 2,222 feet tall to the tip of the building.
So as of now that is the building that is the tallest unless another building gets built even higher than that and I would be very impressed.