Police say their main working hypothesis is that she fell into the River Wyre, and that this is "a tragic case of a missing person".
On Sunday 19 February police recovered a body close to where Ms Bulley was last seen.
Here's a timeline of what we know so far:
Friday 27 January
8.26am - Nicola left her home with her two daughters, dropping them off at school and engaging in a brief conversation with another parent around 15 minutes later.
8:43am - Nicola walked along the path by the River Wyre, having dropped her children off at school.
8:50am (approximately) - A dog-walker, who knows Nicola, saw her walking around the lower field with her dog. Their two dogs interacted briefly before the witness left the field via the river path.
8:53am - She sent an email to her boss.
8:59am - She sent a message to her friends
9.01am - She logged into a Teams call.
9:10am (approximately) - A witness, who knows Nicola, saw her on the upper field walking her dog, Willow.
9.30am - The Teams call ended but Nicola stayed logged on.
9.33am - Nicola’s mobile phone and Willow were found on a bench by the river by another dog-walker.
10.50am - Ms Bulley's family and the school attended by her children were told about her disappearance.
Lancashire Constabulary launched an investigation into Ms Bulley's whereabouts on the same day and appealed for witnesses to contact them.
Lancashire Constabulary deployed drones, helicopters and police search dogs as part of the major missing person operation.
They were assisted by Lancashire Fire and Rescue Service, as well as Bowland Pennine mountain rescue team and the North West underwater search team.
10:30am - Local residents held a meeting at the village hall to organise a search for Ms Bulley.
Superintendent Sally Riley from Lancashire Constabulary said police were "keeping a really open mind about what could have happened", and that they were not treating Ms Bulley's disappearance as suspicious.
Lancashire Constabulary spoke with a potential witness, a man who had been walking a small white fluffy dog near the River Wyre at the time of Ms Bulley's disappearance.
Her family released a statement saying they had been "overwhelmed by the support" in their community, and that her daughters were "desperate to have their mummy back home safe".
Ms Bulley's parents, Ernest and Dot Bulley, spoke about the "horror" they faced over the possibility of never seeing her again.
Lancashire Constabulary spoke with a second witness who they had identified with the help of the public using CCTV but they told police they did not have any further information to aid their inquiry.
Officers from the North West Police Underwater and Marine support unit searched the area close to where Ms Bulley's mobile phone was found, while police divers scoured the River Wyre.
Meanwhile, Ms Bulley's family appealed to the public for help tracing her.
Lancashire Police said they were working on the hypothesis that Ms Bulley may have fallen into the River Wyre.
Ms Riley urged against speculation, but said it was "possible" that an "issue" with Ms Bulley's dog may have led her to the water's edge.
She urged the public to look out for items of clothing Ms Bulley was last seen wearing, and gave an extensive list.
The woman described as a “key witness” by police came forward.
The force insisted she was “very much being treated as a witness” as it warned against “totally unacceptable” speculation and abuse on social media.
Reports emerged that a private underwater rescue team was set to assist police in the search for Ms Bulley.
Underwater search experts arrived to help in the search.
Peter Faulding, the head of private diving team Specialist Group International, said: "If Nicola is here, I'm happy we will find her, if she's in the river."
Ms Bulley’s friends said they hoped the help of a specialist underwater rescue team would give the family answers.
Her partner, Paul Ansell, said in a statement: “It’s been 10 days now since Nicola went missing and I have two little girls who miss their mummy desperately and who need her back.”
Police rejected suggestions she could have been a victim of crime.
Lancashire Police said their extensive inquiries have “so far not found anything of note”.
A team of 40 detectives were working on approximately 500 different lines of inquiry, it was said.
The force urged the public to avoid “distressing” speculation about what may have happened to Ms Bulley.
Elsewhere, underwater search expert Peter Faulding, who was helping to find her, said he did not think the missing mother was in the water.
Mr Ansell spent 10 minutes on the riverbank near the bench where Ms Bulley’s phone was found.
He spoke of the “perpetual hell” of not knowing what had happened.
Mr Faulding said after three unsuccessful days of looking in the water, he was “baffled”.
Search teams were focusing on the 10 miles or so of river downstream of the bench, where the River Wyre empties into the sea at Morecambe Bay.
Lancashire Police was granted a dispersal order to break up groups of people reportedly filming in the village.
Mr Ansell said the family was going through “unprecedented hell”, but that he would never give up hope of finding her.
Emma White, a friend of Ms Bulley, said the search for the missing woman in St Michael’s on Wyre had been “like torture”.
Meanwhile, police urged people to refrain from indulging in commentary and conspiracy theories online.
Friends and family left yellow ribbons with handwritten messages on a bridge close to where she disappeared.
Ribbons with messages including “We need you home Nicola”, “praying for your safe return” and “I love you” were tied to a footbridge over the River Wyre.
A large poster with a photograph of Ms Bulley was also attached to the railings.
Wyre Council removed councillors’ contact details from its website due to “inappropriate emails and phone calls” about Ms Bulley’s disappearance.
It also temporarily removed contact details for “parish and town council members”.
Two people were arrested on suspicion of sending malicious communications.
During a press conference, senior police officers said Ms Bulley was “vulnerable” and classed as a “high-risk” missing person.
They hit out at “false information, accusations and rumours” which had been circulating.
Activity by online amateur sleuths and social media video-makers had meant officers were “distracted significantly”, the force said.
Detective Superintendent Rebecca Smith, the lead investigator, told reporters: “In 29 years’ police service I’ve never seen anything like it.
“Some of it has been quite shocking and really hurtful to the family.”
Home Secretary Suella Braverman demanded an “explanation” from Lancashire Police as to why aspects of Ms Bulley’s private life were disclosed at a press conference, according to a source close to her.
Ms Braverman was reportedly “concerned” after the force told reporters Ms Bulley suffered “some significant issues with alcohol” in the past, which had resurfaced over recent months.
Earlier in the day it emerged Lancashire Police referred itself to the Independent Office for Police Conduct (IOPC) watchdog over contact the force had with her before she vanished.
Earlier in the day her family called for an end to “speculation and rumours” about her private life in a statement.
The decision to reveal the details was also criticised by MPs and campaign groups.
The three-week anniversary of Ms Bulley’s disappearance.
The police’s decision to reveal details of her private life has continued to come under criticism.
Information Commissioner John Edwards said in a statement he would be speaking to Lancashire Police about why it decided to disclose information about her alcohol and HRT issues.
Former victims’ commissioner Dame Vera Baird said the force had made a “sexist” error by disclosing her struggles with alcohol and the menopause.
Wyre Council leader Michael Vincent revealed people in the village where she vanished have employed an external security company and are “scared in their own homes” because of interest in the case.
He also said there are “lessons to be learned” for Lancashire Police but added they had done their best “in difficult circumstances”.
Lancashire Police also said it would hold an internal investigation into Ms Bulley's disappearance which will be conducted by their Head of Crime, Detective Chief Superintendent Pauline Stables.
Lancashire Police say a body has been found in the search for Ms Bulley.
Police were called at 11:36am on Sunday 19 February to reports of a body in the River Wyre.
An underwater search team and specialist officers subsequently attended the scene, entered the water and have recovered a body.
Formal identification is yet to take place.
Lancashire Police said there has been an "unprecedented amount of work" on the investigation, with more than 40 dedicated detectives looking through hundreds of hours of possible leads.
More than 300 premises have been visited and around 1,500 pieces of information have been received.
Extensive searches have been carried out on the River Wyre, with officers searching as far as the sea.
CCTV - Officers have viewed a “substantial amount of CCTV, which has helped them “pin down” some of Ms Bulley’s movements
Dashcam - Due to the lack of CCTV footage on the river path the force has appealed for dashcam footage from motorists and cyclists. Every piece of footage has been reviewed, but none of it has indicated that Ms Bulley was there.
Witnesses - Officers have spoken to a number of dog walkers known to Ms Bulley, who were in the area at the time, described by Det Supt Smith as “key witnesses”.
Digital devices - Officers, along with digital experts, have carried out an “exhaustive amount of work” on Ms Bulley’s phone.
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