As you gain more experience, your prior experience becomes outdated, and doesn't show an accurate picture of your up to date skills. You want to be efficient in

As you gain more experience, your prior experience becomes outdated, and doesn't show an accurate picture of your up to date skills. You want to be efficient in showing the employer the most relevant details of your experience, so they can make their decision faster. The stuff you did 10 years ago may just be a distraction, and may make you look worse than you are today. A page or two should be sufficient in painting a convincing picture of your expertise, even if it isn't comprehensive. After you pass the resume screening, you may want to follow up with a full CV. The difference between a CV and a resume, at least in the US, is that the CV is the unabridged version of your resume, containing all your experience. The resume should be a condensed version of it showing just the most impressive and enticing parts.