There are records of settlements in Pendik going back to the Ancient Macedonians of 4,000 years ago, a Roman settlement in 753 BC, and many more conquests. In 1080, the town was taken over by the Seljuk Turks, and recaptured by the Byzantines in 1086 and so on. During the Byzantine era, the place was called "Pantikion or "Pentikion", and before that "Pantikapion" and "Pantikapeum" (as the town had five walls, or five gates, or both). Pendik was always a retreat from the city, and by the 20th century was peppered with holiday and weekend homes of Istanbul's wealthy.
Until the 1970's Pendik was a rural area, far from the city. Today Pendik is a crowded mix of working class housing (especially further towards the E5 motorway) with more expensive apartments with sea views along the coast. it is a pleasant neighbourhood with wide streets and of course the coastline. There is a busy shopping district with a large street market (on Saturdays), restaurants and movie theaters. It is quite well-served for schools and other amenities and many districts of Pendik have well-established, settled communities.
But Pendik is far from the city and public transport to the city is by slow and meandering buses and minibuses, or by the slow suburban trains to Kadiköy. The coast road is fast but does not carry public transport. You would need to get up before 6am to be at work in the city for 8.30, but many people do. And even more work in the Pendik/Tuzla/Gebze region, which has seen great industrial development in the 90's. This is the main reason for Pendik's population growth.
In the 1990s a mass of refugees who escaped from the war in Bosnia settled in the Pendik district of Sapanbaglari. Apart from naming their streets and shops after their village in Bosnia, these people have blended into the Istanbul working-class lifestyle of the rest of Pendik.
In the late 90's two important private educational institutions were built inland from Pendik, Koç Özel Lisesi and Sabanci University. And the Formula One racetrack is here too. There is a high-speed boat across the Marmara Sea from here to Yalova for people travelling out of the city to Bursa and the Aegean. And Sabiha Gökçen airport is near here.
Pendikspor is a minor league football team which once famously defeated Fenerbahçe.