Street art and graffiti are a part of the modern urban scene that is developed in public spaces. A traditional graffiti artist has primarily used free-hand aerosol paints to make their work, "street art" encompasses many other media and techniques as stencil art, sticker art, street illustrations ect...
The motivation and objectives that drive street artists are as varied as the artists themselves. These days graffiti is seen everywhere you are. You see it on buildings, the metro, pipes, parking lots, school hallways, and anywhere there is possible for a person to make their mark. 
This kind of graffiti and street art is everything from scribbled letters of someone's name to detailed well-thought-out art. Grafitti is very different from where it started. Something that started as an illegal act of vandalism, is now seen as art and is even bought or made by orders. Of course, some graffiti is still considered vandalism, but it is depending on where and why the graffiti is done

But, where did it all start?

The word "Grafitti" is actually originally from the Italian word "Graffito" which means a scratch. This is because the original graffiti was people scratching symbols into the wall, and not painted on. But the word is ultimately derived from the Greek word “graphein,” which means to draw, write or scratch. 

The first time graffiti was mentioned was in 1851, but this art form stems all the way back to the earliest era of humans, during the "old stone age". when humans first made their homes in caves and drew on the cave walls – the first time humans ever expressed themselves artistically even though they were simple drawings of animals and abstract shapes. 

Well, as we know, graffiti has evolved and it really made an impact on society and culture in the 20th century. Even with modern technology enhancements, people are still compelled to leave their mark anywhere they can. 

In the 1960s, a historic world-renowned construction took place. The Berlin wall. Dividing the german capital in two. Although people in East Berlin were not allowed near the wall, those on the west were free to approach the wall. This turned into a carpet of street art and graffiti along the wall. To this day, it’s alive with colorful illustrations of the sentiments of peace and love. Having some of the world's most iconic street art pieces.

The first use of Grafitti how we know it today can be linked back to the early 20th century. Hobos used graffiti to communicate with each other. They used chalk or coal to wite symbols that were unknown to outsiders on train yards, bridges, and other known hobo spots. Some of this reason was to warn each other about strict law enforcement in the area or to recommend a place to work or camp on.

In the late-60s poor kids growing up in the Bronx and Brooklyn used the first to tags to express themselves and get some street fame and cred. By the 1970s artists helped transform graffiti from street art to high art displayed in galleries. The movement had truly expanded before it burst into the ‘80s

In the 1980s, the time when graffiti mecca: New York, had its big boom. The city created some of this style's biggest icons like: Jean-Michel Basquiat, Keith Haring and Futura 2000. All three have very different styles and expressions, but emerged from the same environment and continue to inspire other creatives across the world. 

Grafitti / street art as we know it

Around the 1980s when hip-hop was an up-and-coming music genre, graffiti started to become associated with the new sound and still has strong ties to hip-hop culture. Along with DJing, MCing, and breaking, graffiti is a central part of this culture – with it all being traced back to the Bronx in NYC.
Around the same time that NYC’s graffiti scene was booming, the art was also spreading across the globe. Taggers and artists were making the city their canvas in all cities, including London, Rome, Paris and more.

Now we are in the 90s and graffiti is everywhere and becomes its own art form. Many of the original creators are now growing up and expanding their talents, while a new bunch of kids still starts to work on their writings. 
Grafitti and street art have now been so big that Custom-made spraypaint has come to the market. This allowed artists to do more difficult paintings and increasing the quality of these works of art.
It was during this time new techniques were used. Artists now using stickers and stencils to apply their art, which allowed them to create elaborate drawings that could easily be prepared in advance and then applied quickly, which was ultra important to avoid getting caught by officials

We are now in the 2000s and these urban forms of expression are more appreciated than ever. 
Collectors were now trying to commission some of the hottest street artists for personal work.
street artists are even hired to decorate large building walls. Since the need for unfolding and expression is just as important and common today, and graffiti is still not allowed in public places, it is no wonder that graffiti artists use cover artist names. 

Photograph of Street art made in the 1960s. This part of the wall is now protected. It communicates well and expresses the frustration of what time Berlin was in at that time.

Picture taken by: Japleenpasricha
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Baltimore's Graffiti Alley.
Example of street Graffiti, most often in backyards and outskirts of cities.

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A beautiful example of street art using new techniques for creating masterpieces. 

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New style street art, creating creative, new iconic styles. 
Made by two artist calling itself:  Billy.

-linked at the bottom. 
Artist have lots of creative designs in different forms. (walls, shoes, phone cases.. and more) 

Often vibrant colors
"3D" lettering
black outlining
special, innovative -designs
Stansil styles

Everything you can think of, or feel. 

Using every color imaginable. Every artists has its own colour palette. 

Often bright colors to make concrete and bricks pop!

When What Why
1961-1991 Berlin wall The Berlin Wall became an art mecca for graffiti and street artists. Protests against Berlin's governance.

In his short life, Jean-Michel Basquiat was a pop icon, cultural figure, graffiti artist, musician, and neo-expressionist painter.

Became one of Graffitis Bic icons.

One of the few women among the original graffiti artists of the 1970s and’80s, Lady Pink was born Sandra Fabara in Ecuador and raised in NYC, where she painted subway trains between 1979 and 1985.  Her works, know for their strong feminist/latina edge, resides in the collection of such major institutions as Whitney Museum, The Metropolitan Museum New York City, the Brooklyn Museum and the Groningen Museum in the Netherlands.

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Gathered my information from the following sites, and I recommend taking a peak on these good sites: 

Pictures:     (Grafitti in the streets)             (Berlin wall picture)              (New art, Girl with birds)         (New style, creative Dooddeling)