ABC loved both the show pitch from Christopher Lloyd and Steven Levitan (a series with three family structures: a traditional similar-age WASP couple with kids, a May-December marriage with a step-kid, and a same-sex relationship who had just adopted a daughter) and the pilot episode so much that the network took the unprecedented step of showing the entire pilot at the upfront meetings for advertisers. It was so well-received that ABC then renewed the show for a 2nd season without even waiting for the Nielsen ratings for the pilot airing (which were excellent).
Julie Bowen, who plays the character Claire, was 8 and a half months pregnant with twins. Her stomach is hidden by various things such as laundry or cereal boxes but can be seen briefly when she is first seen calling the kids downstairs for breakfast.
When Phil is saying he knows all the texting abbreviations and says wtf is "why the face" instead of the alternative, was an improvisation that actor Alan Tudyk did when auditioning for the role of Phil. The producers liked it so much they asked his permission to use it during filming.
Ed O'Neill has a daughter named Claire in real life, and his other daughter is named Sofia, the real name of his TV wife.
The pilot script was originally titled "My American Family"