A convoy carrying medical supplies enters Gaza through the Erez crossing
The BBC News website looks at what is and is not allowed into Gaza via the Israeli controlled crossing points.
Basic food and medical items are allowed in. Very few people and virtually no raw materials and building materials are allowed in.
Apart from a core list of humanitarian basics - fruit, dairy, flour, oil, sugar, meat, rice - items have to be approved on a case-by-case basis.
The list of items allowed in changes over time. During the six-month ceasefire in 2008, items such as clothes, shoes, car parts and agricultural supplies entered the Gaza Strip at times.
This has not been the case since the Israeli assault on Gaza started in late December 2008.
Since the conflict, shipments have mainly been limited to food, medical supplies, plastic sheeting, blankets, mattresses and hygiene and cooking kits.
The UN relief agency for Palestinian refugees says macaroni, lentils, fruit juice, sweets and paper for school books have been rejected in recent weeks. Israel says pasta, lentils and paper are now being allowed in.
Israel says building materials such as pipes and cement may be used to manufacture rockets and rocket launch pads.
Except for supplies for a handful of specific, internationally-managed projects, building materials have not been allowed into Gaza since June 2007, when Hamas took over the strip by force.
The Rafah crossing on Gaza's border with Egypt is closed - opening only to allow the occasional passage of people for medical or humanitarian reasons.
Anything else that enters Gaza comes through the tunnels that run under the border with Egypt.
One of the stated aims of the Israeli assault on Gaza was to stop the traffic through the tunnels. Israeli air strikes continue to target these.